fix(python): preserve original JSON keys in Data shim round-trips

[syf2211]

Summary

Fixes Data.from_dict().to_dict() corrupting JSON keys that contain common abbreviations (e.g. userURL, sessionID, OAuthToken).

Motivation

The Data compatibility shim converts inbound JSON keys to snake_case for attribute access, then uses heuristic _compat_to_json_key when serializing back. That converter cannot reconstruct abbreviation-heavy camelCase, so keys were mutated on round-trip. This breaks consumers of unknown/custom event payloads that log, cache, or echo events.

Fixes #1138

Changes

• Store the original JSON key per field in Data._json_keys during from_dict()
• Prefer the stored JSON key in to_dict(); fall back to _compat_to_json_key for manually constructed Data(**kwargs)
• Update the Python codegen template in scripts/codegen/python.ts and regenerate session_events.py

Tests

• uv run pytest test_event_forward_compatibility.py -v — 11 passed
• uv run ruff check test_event_forward_compatibility.py — passed
• Added test_data_shim_preserves_abbreviation_json_keys_on_round_trip covering the keys cited in the issue

Notes

• Unknown event types parsed via SessionEvent.from_dict already use RawSessionEventData (verbatim raw). This fix targets the Data shim used for backward-compatible/manual payloads.
• Pre-existing key-collision edge case (userURL vs userUrl both mapping to user_url) is unchanged.
• Reviewed with composer-2.5 subagent: APPROVE