Gigachat 3 tool parser and tests

[Mishusha]

This PR adds a tool parser for parsing the function calls made by the Gigachat 3 models.
Models can generate only one function call using format:

{text}<|message_sep|>\n\nfunction call<|role_sep|>\n{json}
Where <|message_sep|>\n\n and <|role_sep|>\n are special tokens.

[aldehir]

We should start transitioning to the PEG parser approach. This one looks very similar to the new mistral-3 series, there is already a parser out there to reference. The difference is you'll need to match the name within the JSON instead of outside of it, but it should be easy with the schema(), json() and json_member() helpers.

[pwilkin]

Like @aldehir mentioned, please use the PEG parser for the implementation, we are phasing out the old parser. If you need an example, check out the Ministral 3 template.

[Mishusha]

Got it, thanks, I took it to work)