Refactor calculators to emit event-derived stats

[colonelpanic8]

Summary

• Adds append-only calculator event streams with per-update new event accessors.
• Moves stat aggregation out of calculators into event-derived accumulator/projection modules.
• Threads boost and core match stats events through timeline event output so serialized partial sums can be reconstructed from events.

Why

Calculators should be responsible for detecting events and state changes. Summary stats are now derived separately from those event streams, which keeps detection logic and aggregation logic easier to reason about independently.

Validation

• just fmt-check
• just clippy
• cargo check
• cargo test match_stats
• cargo test test_core_events_reconstruct_serialized_partial_sums
• cargo test

Note: one earlier full cargo test run hit a non-reproduced native allocator abort in post_eac_replay_fixture_test. The isolated failing test and a full rerun both passed cleanly.