Exposes raw `DataLoader`s to the Python SDK through 2 new methods:
`RecordingStream.log_file_from_path` &
`RecordingStream.log_file_from_contents`.

Everything streams asynchronously, as expected.

There's no way to configure the behavior of the `DataLoader` at all,
yet. That comes next.

```python
rr.log_file_from_path(filepath)
```

![image](https://github.com/rerun-io/rerun/assets/2910679/0fe2d39c-f069-44a6-b836-e31001b3adaa)


---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355

Exposes raw `DataLoader`s to the C++ SDK through 2 new methods:
`RecordingStream::log_file_from_path` &
`RecordingStream::log_file_from_contents`.

Everything streams asynchronously, as expected.

There's no way to configure the behavior of the `DataLoader` at all,
yet. That comes next.

:warning: I'm carrying bytes around in a `string_view` (see `rr_bytes`)
and related, and the internet has been unhelpful to tell e whether I
should or shouldn't.

```cpp
rec.log_file_from_path(filepath);
```

![image](https://github.com/rerun-io/rerun/assets/2910679/1933f08b-1b2b-483b-9576-ce2e0421cb62)



---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355

---------

Co-authored-by: Andreas Reich <andreas@rerun.io>

Introduces `RecordingStream::clone_weak`, so `DataLoader` threads
started from the SDK don't prevent the recording from flushing once
`main` goes out of scope, all the while making sure that `DataLoader`s
run to completion.


![image](https://github.com/rerun-io/rerun/assets/2910679/94bf7b16-cf9b-40ce-a190-d255328af3f8)


- Mitigates #5335 

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355

Adds new `RecommendedLoadSettings` that gets passed to all `DataLoader`s
-- builtin and external -- in order to customize their behaviors.

This includes:
- A recommended recording ID
- The ID of the currently opened recording in the viewer (not
implemented)
  - Related: #5350
- A recommended entity path prefix
- A recommended timepoint

```bash
cargo r -p rerun-loader-rust-file -- run_wasm/src/main.rs  --recording-id this-one --entity-path-prefix a/b/c  --time sim_time=1000 --time wall_time=1709204046 --sequence sim_frame=42 | rerun -
```

![image](https://github.com/rerun-io/rerun/assets/2910679/631d9798-c198-4e86-b6f8-32d0b849e7b2)


Checks:
- [x] external loader ran manually (`loader | rerun`)
- [x] external loader via rerun (`rerun xxx.rs`)
- [x] log_file with external loader (`log_file xxx.rs`)

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355

This makes the `log_file` APIs behave more like the standard `log` APIs;
i.e. they inherit the state of their associated `RecordingStream`
(app_id, rec_id, timepoint, etc...).

Also inherit the application ID while we're at it.

Makes the API much nicer to use _and_ much more consistent with the
rest.

Checks:
- [x] external loader ran manually (`python loader | rerun`)
- [x] external loader via rerun (`rerun xxx.py`)
- [x] log_file with external loader (`log_file xxx.py`)
- [x] external loader ran manually (`loader | rerun`)
- [x] external loader via rerun (`rerun xxx.rs`)
- [x] log_file with external loader (`log_file xxx.rs`)

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355
- #5379
- #5361
- #5388

---------

Co-authored-by: Andreas Reich <andreas@rerun.io>

Introduces the new `DataLoaderSettings` business to C++ and update
examples accordingly (`external_data_loader` & `log_file`).

```bash
./build/debug/examples/cpp/log_file/example_log_file --recording-id this-one --entity-path-prefix a/b/c  --time sim_time=1000 --time wall_time=1709204046 --sequence sim_frame=42 rerun_cpp/tests/main.cpp | rerun -
```

![image](https://github.com/rerun-io/rerun/assets/2910679/b979a24c-29b6-473b-91b1-de3832bea436)


Checks:
- [x] external loader ran manually (`loader.exe | rerun`)
- [x] external loader via rerun (`rerun xxx.cpp`)
- [x] log_file with external loader (`log_file xxx.cpp`)

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355
- #5379
- #5361
- #5388

I guess that's good enough 🤷. I don't know, my brain has been
completely friend by C++ non-sense all day.

This includes a fix to make sure that a viewer that was spawned from the
python SDK is still allowed to spawn dataloaders implemented in python
(`RERUN_APP_ONLY` shenaniganeries).

- Fixes #4526 

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355
- #5379
- #5361
- #5388