What this PR does / why we need it:

A stored NaN or +/-inf float value makes POST /get-online-features fail with HTTP 500 (ValueError: Out of range float values are not JSON compliant). _value_to_native returns raw Python floats, and JSONResponse serializes with allow_nan=False, so one non-finite value fails the whole multi-feature response. The SDK get_online_features().to_dict() path serves the same value fine. /search and /retrieve-online-documents share convert_response_to_dict and are affected too.

This PR encodes non-finite values as the protobuf JSON mapping strings "NaN", "Infinity" and "-Infinity". This applies to:

• scalar double_val / float_val
• double_list_val, float_list_val, double_set_val, float_set_val (element-wise)

Finite values are unchanged, and lists without non-finite values still go through a plain list(...). Nested list_val / map_val / struct_val values get the fix through the existing recursion. The convert_response_to_dict docstring documents the encoding.

If maintainers would rather emit null for non-finite values (the behaviour while ORJSONResponse was in use), this is a one-line change in _float_to_native.

Not covered here: RemoteOnlineStore._build_online_response_from_json infers value types from the JSON, so it would read the encoded strings as strings and rejects a list that mixes numbers and strings. This path already failed before (the server returned 500), and null would not round-trip through it either. I can follow up on the client side once the encoding is settled.

Which issue(s) this PR fixes:

No separate issue; the bug is described above.

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

New tests:

• tests/unit/test_feature_server.py::test_get_online_features_serves_non_finite_float[inf|-inf]: writes +/-inf to the online store, checks that the SDK serves it, then checks that /get-online-features returns 200 with "Infinity" / "-Infinity" and status PRESENT.
• tests/unit/test_feature_server_utils.py: covers NaN/inf/-inf for double_val and float_val, the four float/double list and set types, and a json.dumps(..., allow_nan=False) round trip of convert_response_to_dict.

From sdk/python:

python -m pytest tests/unit/test_feature_server_utils.py tests/unit/test_feature_server.py -q

• Without the fix (the tests only): 13 failed, 97 passed. Every new test fails, and the endpoint test fails with assert 500 == 200 / Out of range float values are not JSON compliant.
• With the fix: 110 passed.

tests/unit/test_proto_json.py, tests/unit/test_feature_server_async.py and tests/unit/infra/feature_servers/test_mcp_server.py also pass (28 passed). ruff check and ruff format --check (0.16.9) are clean on the changed files.

Misc