feat(core)!: raise exception if type value is different in dicts to merge

[cbornet]

• Solves a TODO that was planned for v0.3 but still hasn't been done. See core[patch]: dont mutate merged lists/dicts #25858
• Removes commented code (ruff rule ERA)
• Targets v1.0 as this is breaking.

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ready	Preview	Comment	Sep 10, 2025 5:10pm

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32888 will not alter performance

_{Comparing cbornet:merge_dict (60c6521) with wip-v1.0 (544b08d)}

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Summary

✅ 13 untouched benchmarks

[cbornet]

cc @baskaryan as you introduced the TODO.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32888 will not alter performance

_{Comparing cbornet:merge_dict (60c6521) with wip-v1.0 (544b08d)}

Summary

✅ 14 untouched benchmarks

[cbornet]

Some tests fail:

assert AIMessageChunk(
        content=[{"index": 0, "text": "I am", "type": "text_block"}]
    ) + AIMessageChunk(
        content=[{"index": 0, "text": " indeed.", "type": "text_block_delta"}]
    ) == AIMessageChunk(
        content=[{"index": 0, "text": "I am indeed.", "type": "text_block"}]
    ), (
        "Concatenating when both content arrays are dicts with the same index "
        "and different types should merge without updating type"
    )

It seems the merge_dicts should now allow to merge with different types ?

So should we:

1. remove the TODOs and related code (basically revert core[patch]: dont mutate merged lists/dicts #25858) ?
2. or modify the AIMessageChunk tests ?
3. or have an optional param in merge_dicts to allow merging dicts with different types ?
4. other ?

[cbornet]

So should we:
remove the TODOs and related code (basically revert #25858) ?
or modify the AIMessageChunk tests ?
or have an optional param in merge_dicts to allow merging dicts with different types ?
other ?

@eyurtsev @mdrxy can I have your opinion on this ?