fix: record events in mjai_log for apply_event/observe_event (#184)

[smly]

Fixes #184

apply_event() and observe_event() updated game state correctly but did not push events to mjai_log, causing get_viewer() to show only the constructor's initial events (typically just start_game, start_kyoku, tsumo).

[Copilot]

Pull request overview

This PR fixes a viewer/debugging regression where MJAI events applied via the Python API (apply_event() / observe_event()) updated state but were not recorded into mjai_log, causing get_viewer() to show only constructor-emitted events.

Changes:

• Push applied/observed MJAI events into the underlying game state’s mjai_log (and per-player logs) so the viewer can render full replays.
• Clear constructor-emitted logs when a user replays from a new start_game event.
• Add regression tests covering mjai_log accumulation for both 4P and 3P, and for both apply_event() and observe_event().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
riichienv-python/src/env.rs	Records applied/observed MJAI events into mjai_log and clears stale constructor logs on start_game.
tests/env/test_apply_event_mjai_log.py	Adds regression tests to ensure mjai_log is populated correctly for replay + viewer use.

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[Copilot]

Pull request overview

This PR fixes MJAI event logging for the Python RiichiEnv wrapper so that events applied via apply_event() / observe_event() are recorded into mjai_log, enabling get_viewer() to display replayed/custom logs correctly (regression for #184).

Changes:

• Add shared Rust-side helper logic to “parse → (optional start_game reset) → apply → push into mjai_log” for both apply_event() and observe_event().
• Add parse_mjai_event() helper to avoid redundant JSON parsing.
• Add Python regression tests covering mjai_log recording for both 4P and 3P, for both apply_event() and observe_event().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
riichienv-python/src/env.rs	Refactors event parsing and ensures apply_event()/observe_event() push MJAI events into the core state’s mjai log (with start_game log reset behavior).
tests/env/test_apply_event_mjai_log.py	Adds regression tests asserting that events applied/observed are recorded into env.mjai_log in correct order and with expected fields.

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