feat: add Hermes tool call parser

[scubamount]

Summary

Adds fallback support for the Hermes-style/Liquid tool call wire format:

<|tool_call_start|>[function_name(arg=value)]<|tool_call_end|>

Some clients/agents emit tool calls using these markers instead of oMLX's currently supported XML/prose bracket formats. Without this fallback, oMLX can surface raw marker text to users instead of returning structured tool calls.

This PR:

• parses Hermes-style JSON payloads inside <|tool_call_start|>...<|tool_call_end|>
• parses Python-expression-like bracket payloads such as [read_file(path='/tmp/a.log')]
• supports multiple calls in one Hermes block via AST parsing, e.g. [tool_a(...), tool_b(...)]
• suppresses Hermes start/end markers during streaming even when tokenizer metadata is absent
• suppresses orphan/split Hermes closing markers so <|tool_call_end|> cannot leak if it arrives without a visible open marker
• strips any remaining complete Hermes envelopes from final assistant text if parsing fails
• classifies LFM2 text checkpoints as LLMs instead of embeddings by treating lfm2 as ambiguous and relying on architecture/name checks

Verification

/opt/homebrew/opt/python@3.12/libexec/bin/python3 -m pytest tests/test_tool_calling.py -q
161 passed in 0.16s

/opt/homebrew/opt/python@3.12/libexec/bin/python3 -m pytest tests/test_model_discovery.py -q
119 passed in 0.16s

[scubamount]

Cross-ref: this PR is the server-side counterpart to NousResearch/hermes-agent#37229 (fix: normalize local tool JSON fallbacks).

These two PRs are co-dependent:

• omlx#1596 (this PR): parses Hermes-style <|tool_call_start|>...<|tool_call_end|> markers at the inference server layer, so OMLX returns structured tool calls instead of raw marker text.
• hermes-agent#37229: normalizes local-model assistant JSON with commands/tools_used into OpenAI-style tool calls on the hermes-agent client side.

Without both, local model tool calling is broken:

• Without omlx#1596 → OMLX leaks raw Hermes markers to hermes-agent
• Without hermes-agent#37229 → hermes-agent cannot normalize the mixed JSON/bracket payloads that local models emit

Both should merge together for a complete fix.