Issue NFIBrokerage#96

Passing a `raw?: true` option to `Spear.append/3` or `Spear.Client/append`
continued to return `:ok` instead of `{:ok, AppendResp.t()}`.

This contradicted the docs and the `Spear.append_batch/5` behaviour.

Solution:

This commit adds the conditional case in `Spear.append/3`
to return `{:ok, AppendResp.t()}` when `raw?` is `true`.

`Spear.Client.append` will also be fixed as a result.

Additional Notes:

* Added to `SpearTest`: to test `append/3` for both raw true and false
* Added to `SpearTest`: to test `append_batch/5` for both raw true and false.
* Updated the `Spear.append/3` type spec to add the missing
  `{:ok, AppendResp.t()}` return type.
* Updated the `Spear.Client.append/3` and `Spear.Client.append/4`
  callback specs to add the missing `{:ok, AppendResp.t()}` return type.

adding compat tag to the append_batch tests,
which weren't carried over from the append_batch test
copy pasting.

Fixes a `mix format --check-formatted` issue in `spear_test.exs`
that was caught with Elixir 1.14, vs not catching in Elixir 1.16.2.

Before, it was pulling out the "result", now we're returning
the raw proto

1. fixes the unintentionally added extra nesting of `{:ok, {:ok, resp}}`
  Instead, when success and raw flag set, returns `{:ok, raw_response_pb}`.
2. Adds the extra raw response check so that `append/3` returns
    `{:error, raw_unexpected_version_response_pb}` if there is the wrong
    expected version response AND raw flag set.

If I just did

```
  {:ok, response} when raw? == true ->
        {:ok, response}
```

An `{:ok, raw_unexpected_version_response_pb}` could have been returned
on unexpected version error response.

`raw?: true` cases regardless of `:success` or `:wrong_expected_version`

Also, cleans up the test cases to use `Streams.append_resp`
pattern matching.