**Motivation**

Being able to store and fetch blocks from the db via `Store` api

**Description**

* Replace `Transaction::encode` with `Transaction::encode_with_type`
logic (Reasoning: We cannot decode the transactions without knowing
their type with the current behaviour, making it impossible to implement
`RLPDecode` for `Transaction`)
* Implement `RLPDecode` for `Transaction` (Using the logic that was
previoulsy used in `EncodedTransaction::decode` (payload module))
* Implement `RLPDecode` for `Withdrawal`, `BlockHeader` and `BlockBody`
* Add the folloewng methods to `Store` and `StoreEngine`:
`add_block_header`, `add_block_body`, `get_block_header`,
`get_block_body`, and implement them for `InMemory` and `Libmdbx` engine
types

<!-- A clear and concise general description of the changes this PR
introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes None, but is needed for #145

**Motivation**

Currently, the `handle_http_requests` doesn't allow us to return an
error when handling requests. This can be solved by handling them via a
`map_requests` function like in `handle_authrpc_requests`. While
`handle_authrpc_requests` handles comunication between clients and
`handle_http_requests` handles comunication between the client and
users, there are a lot of requests that are handled by both of them. As
they both use the same request format, there is little reason to
implement two different functions to handle the same requests in the
same way. We can use `map_requests` to handle both auth_rpc and http
requests, and then implement a second handler (such as
`map_internal_requests`) to handle auth_prc-specific requests.

<!-- Why does this pull request exist? What are its goals? -->

**Description**

Replaces `handle_http_requests` request handling with a call to
`map_requests`

<!-- A clear and concise general description of the changes this PR
introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes None, but addresses comment on #145

Based on #145 

**Motivation**

Being able to respond to `eth_getBlockTransactionCountByNumber` requests
via rpc
<!-- Why does this pull request exist? What are its goals? -->

**Description**

Add rpc endpoint `eth_getBlockTransactionCountByNumber`

<!-- A clear and concise general description of the changes this PR
introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes #33

---------

Co-authored-by: Tomás Grüner <47506558+MegaRedHand@users.noreply.github.com>

Based on #145 

**Motivation**

Support rpc endpoint `eth_getBalance`
**Description**

Add rpc endpoint `eth_getBalance`

<!-- A clear and concise general description of the changes this PR
introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes #36