For this we make the assumption that the keys are unique.

Note: this does not hold universally, yet. Implementations in
`nu-protocol` use an all key removal on the basis of retain in certain
places. (e.g. used by `reject` under the hood)

See nushell#8446 for this defensiveness

# Description
Pretty much all operations/commands in Nushell assume that the column
names/keys in a record and thus also in a table (which consists of a
list of records) are unique.
Access through a string-like cell path should refer to a single column
or key/value pair and our output through `table` will only show the last
mention of a repeated column name.

```nu
[[a a]; [1 2]]
╭─#─┬─a─╮
│ 0 │ 2 │
╰───┴───╯
```

While the record parsing already either errors with the
`ShellError::ColumnDefinedTwice` or silently overwrites the first
occurence with the second occurence, the table literal syntax `[[header
columns]; [val1 val2]]` currently still allowed the creation of tables
(and internally records with more than one entry with the same name.

This is not only confusing, but also breaks some assumptions around how
we can efficiently perform operations or in the past lead to outright
bugs (e.g. #8431 fixed by #8446).

This PR proposes to make this an error.
After this change another hole which allowed the construction of records
with non-unique column names will be plugged.

## Parts
- Fix `SE::ColumnDefinedTwice` error code
- Remove previous tests permitting duplicate columns
- Deny duplicate column in table literal eval
- Deny duplicate column in const eval
- Deny duplicate column in `from nuon`

# User-Facing Changes
`[[a a]; [1 2]]` will now return an error:

```
Error: nu::shell::column_defined_twice

  × Record field or table column used twice
   ╭─[entry #2:1:1]
 1 │ [[a a]; [1 2]]
   ·   ┬ ┬
   ·   │ ╰── field redefined here
   ·   ╰── field first defined here
   ╰────
```

this may under rare circumstances block code from evaluating.

Furthermore this makes some NUON files invalid if they previously
contained tables with repeated column names.

# Tests + Formatting
Added tests for each of the different evaluation paths that materialize
tables.

This breaks two tests

Using `Record::remove` assumes that the keys are all unique. The current
implementation since nushell#8446 uses the less efficient way of going over the
whole record with `.retain` to deal with repeated keys.

Culprit in the example is the table literal

# Description
Pretty much all operations/commands in Nushell assume that the column
names/keys in a record and thus also in a table (which consists of a
list of records) are unique.
Access through a string-like cell path should refer to a single column
or key/value pair and our output through `table` will only show the last
mention of a repeated column name.

```nu
[[a a]; [1 2]]
╭─#─┬─a─╮
│ 0 │ 2 │
╰───┴───╯
```

While the record parsing already either errors with the
`ShellError::ColumnDefinedTwice` or silently overwrites the first
occurence with the second occurence, the table literal syntax `[[header
columns]; [val1 val2]]` currently still allowed the creation of tables
(and internally records with more than one entry with the same name.

This is not only confusing, but also breaks some assumptions around how
we can efficiently perform operations or in the past lead to outright
bugs (e.g. nushell#8431 fixed by nushell#8446).

This PR proposes to make this an error.
After this change another hole which allowed the construction of records
with non-unique column names will be plugged.

## Parts
- Fix `SE::ColumnDefinedTwice` error code
- Remove previous tests permitting duplicate columns
- Deny duplicate column in table literal eval
- Deny duplicate column in const eval
- Deny duplicate column in `from nuon`

# User-Facing Changes
`[[a a]; [1 2]]` will now return an error:

```
Error: nu::shell::column_defined_twice

  × Record field or table column used twice
   ╭─[entry nushell#2:1:1]
 1 │ [[a a]; [1 2]]
   ·   ┬ ┬
   ·   │ ╰── field redefined here
   ·   ╰── field first defined here
   ╰────
```

this may under rare circumstances block code from evaluating.

Furthermore this makes some NUON files invalid if they previously
contained tables with repeated column names.

# Tests + Formatting
Added tests for each of the different evaluation paths that materialize
tables.

# Description
Pretty much all operations/commands in Nushell assume that the column
names/keys in a record and thus also in a table (which consists of a
list of records) are unique.
Access through a string-like cell path should refer to a single column
or key/value pair and our output through `table` will only show the last
mention of a repeated column name.

```nu
[[a a]; [1 2]]
╭─#─┬─a─╮
│ 0 │ 2 │
╰───┴───╯
```

While the record parsing already either errors with the
`ShellError::ColumnDefinedTwice` or silently overwrites the first
occurence with the second occurence, the table literal syntax `[[header
columns]; [val1 val2]]` currently still allowed the creation of tables
(and internally records with more than one entry with the same name.

This is not only confusing, but also breaks some assumptions around how
we can efficiently perform operations or in the past lead to outright
bugs (e.g. nushell#8431 fixed by nushell#8446).

This PR proposes to make this an error.
After this change another hole which allowed the construction of records
with non-unique column names will be plugged.

## Parts
- Fix `SE::ColumnDefinedTwice` error code
- Remove previous tests permitting duplicate columns
- Deny duplicate column in table literal eval
- Deny duplicate column in const eval
- Deny duplicate column in `from nuon`

# User-Facing Changes
`[[a a]; [1 2]]` will now return an error:

```
Error: nu::shell::column_defined_twice

  × Record field or table column used twice
   ╭─[entry nushell#2:1:1]
 1 │ [[a a]; [1 2]]
   ·   ┬ ┬
   ·   │ ╰── field redefined here
   ·   ╰── field first defined here
   ╰────
```

this may under rare circumstances block code from evaluating.

Furthermore this makes some NUON files invalid if they previously
contained tables with repeated column names.

# Tests + Formatting
Added tests for each of the different evaluation paths that materialize
tables.