[Bugfix] Parse MiniMax M3 streaming reasoning by text markers

[Palaiologos1453]

Fixes #45687.

This reopens the MiniMax M3 streaming reasoning fix against main. The earlier PR #45713 targeted m3_release, but that base branch was deleted after MiniMax M3 landed in main via #45381, so GitHub closed the PR automatically.

MiniMax M3 streaming reasoning markers may be generated as visible marker text even when the tokenizer exposes <mm:think> / </mm:think> as vocab entries. The previous streaming parser only checked for the single marker token IDs, so split-token marker text fell through as delta.content and reasoning never populated delta.reasoning.

This change:

• extracts streaming reasoning/content by comparing visible text segments around MiniMax M3 markers
• keeps reasoning-end state aligned with the text parser so tool parsing can start after a split-token end marker
• updates token-id helper methods to recognize encoded marker sequences
• adds regression coverage where marker vocab entries exist but runtime marker IDs are split

Verification:

• git diff --check HEAD~1..HEAD
• python -m ruff check vllm/reasoning/minimax_m3_reasoning_parser.py tests/reasoning/test_minimax_m3_reasoning_parser.py
• python -m ruff format --check vllm/reasoning/minimax_m3_reasoning_parser.py tests/reasoning/test_minimax_m3_reasoning_parser.py
• python -m py_compile vllm/reasoning/minimax_m3_reasoning_parser.py tests/reasoning/test_minimax_m3_reasoning_parser.py

I could not run the target pytest locally because this Windows checkout is missing transformers:
ModuleNotFoundError: No module named 'transformers'.

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[Palaiologos1453]

Hi maintainers, this PR reopens #45713 against main after the original m3_release base branch was deleted. It fixes the MiniMax M3 streaming reasoning leak reported in #45687.

Could a maintainer add verified or ready if the scope looks reasonable so CI can proceed? Thanks.

[jinbagi]

@DarkLight1337

[jinbagi]

@jeejeelee

[BugenZhao]

LGTM as a quick unblock. In the long term, we should probably consider reworking it entirely with the newly introduced parser engine.

[jinbagi]

@Palaiologos1453