Fix Gemma4 tool parser: support hyphenated function names and braces in string args

[AkashKhamkar]

Problem

Two bugs in mlx_lm/tool_parsers/gemma4.py caused ValueError: No function provided
when parsing certain valid Gemma 4 tool calls:

1. Hyphenated function names — the regex used \w+ which doesn't match -,
   so tools named e.g. manim-video would always fail to parse.

2. Braces inside string arguments — the brace-balancing regex treated {/}
   inside <|"|>...<|"|> string literals as structural braces, breaking the match
   when arguments contained code snippets, markdown, or any text with {}.

Both caused an unhandled exception that crashed the server request.

Fix

• [\w-]+ instead of \w+ for function name matching
• Regex is now string-aware: <|"|>...<|"|> literals are matched atomically
  so braces inside them don't affect brace-balance counting
• ToolFormatter.__call__ in server.py now catches parse errors gracefully
  instead of crashing the request

Tests

Added two test cases to tests/test_tool_parsing.py covering both bugs.

[AkashKhamkar]

@angeloskath would you mind taking a look when you get a chance?

[AkashKhamkar]

hey @kernelpool can you take a look at this if possible thanks :)

[angeloskath]

Looks great thanks!