fix(serializer): handle NaN/Inf floats nested in pydantic models

[Shailendra005]

What does this PR do?

EventSerializer's BaseModel branch returned obj.model_dump() directly, so non-finite floats (NaN/Inf) nested inside a pydantic model skipped the NaN/Inf-to-string conversion that the manual dict/list recursion applies. Python's json C-encoder then emitted bare NaN/Infinity tokens — invalid JSON that the ingestion server's strict parser rejects. This affects the core tracing path (span input/output/metadata serialization).

Fix: recurse the dumped model back through default() (return self.default(obj.model_dump())) so nested non-finite floats get the same safe-string handling as every other path. Behavior for datetimes, enums, UUIDs, dataclasses, media refs, etc. is unchanged (they continue to flow through default()).

Type of change

• Bug fix

Verification

uv sync --locked
uv run --frozen pytest tests/unit/test_serializer.py tests/unit/test_json.py   # 38 passed
uv run --frozen ruff check langfuse/_utils/serializer.py tests/unit/test_serializer.py
uv run --frozen ruff format --check langfuse/_utils/serializer.py tests/unit/test_serializer.py
uv run --frozen mypy langfuse/_utils/serializer.py --no-error-summary

Added regression test test_pydantic_model_with_non_finite_floats which fails on main (bare NaN emitted) and passes with this change.

Checklist

• I self-reviewed the diff.
• I added or updated tests for behavior changes.
• I did not hand-edit generated files.
• I did not commit secrets or credentials.

Closes langfuse/langfuse#16048

Greptile Summary

The PR fixes serialization of non-finite floats inside Pydantic models by recursively normalizing model_dump() output before JSON encoding.

• Converts nested NaN, Infinity, and -Infinity values to safe string tokens.
• Adds a regression test that validates output with strict JSON parsing.

Confidence Score: 5/5

The PR appears safe to merge, with the changed Pydantic serialization path consistently applying the existing JSON-safe normalization.

The recursive call processes dumped model dictionaries and sequences through established serializer branches, and the regression test verifies that non-finite floats no longer reach the JSON encoder as invalid bare constants.

_{Reviews (1): Last reviewed commit: "fix(serializer): handle NaN/Inf floats n..." | Re-trigger Greptile}

Context used:

• Knowledge Base — Utils and Support Types

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