docs: refresh README and CLAUDE.md; add ingest benchmark

The CLAUDE.md architecture section still described the pre-redesign engine:
its data flow named `Batch`, `Agent`, `Player` and `message.rs`, none of
which have existed since T2, and the public API it listed did not match
`lib.rs`. It is the first thing a fresh session reads, so it was actively
misleading. Rewritten against the current module layout, with the invariants
that are easy to violate — ties needing a positive `p_draw`, NaN never being
convergence, log-space evidence, color contiguity, `forbid(unsafe_code)`,
and ingestion-order equivalence — written down.

The README Todo list had five entries that were already done, including
"Time needs to be an enum": `Time` has been a trait since T2, and the
`batch::compute_elapsed()` it pointed at no longer exists. The genuinely
open item — cross-checking `quality()` against sublee/trueskill — stays.

`benches/ingest.rs` measures one-event-per-call against a single batched
call. The rest of the suite only measured batched construction, which is why
the quadratic fixed earlier on this branch went unnoticed for so long.

`TimeSlice::log_evidence` also hashes its target set once instead of
scanning the slice per player per event, so `log_evidence_for` with many
keys is no longer quadratic.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DnsaJg74eNSva3PJjK2eej

README.md

@@ -96,8 +96,8 @@ h.converge().unwrap();
 
 - [x] Implement approx for Gaussian
 - [x] Add more tests from `TrueSkillThroughTime.jl`
-- [ ] Add tests for `quality()` (Use [sublee/trueskill](https://github.com/sublee/trueskill/tree/master) as reference)
-- [ ] Benchmark Batch::iteration()
-- [ ] Time needs to be an enum so we can have multiple states (see `batch::compute_elapsed()`)
-- [ ] Add examples (use same TrueSkillThroughTime.(py|jl))
-- [ ] Add Observer (see [argmin](https://docs.rs/argmin/latest/argmin/core/trait.Observe.html) for inspiration)
+- [x] Generalise a time axis — `Time` is now a trait (`Untimed`, `i64`), not an enum
+- [x] Add examples (`examples/atp.rs`, `examples/scored.rs`)
+- [x] Add Observer (`Observer` / `NullObserver`)
+- [x] Benchmark the inference loop (`benches/batch.rs`, `benches/history_converge.rs`, `benches/ingest.rs`)
+- [ ] Cross-check `quality()` against [sublee/trueskill](https://github.com/sublee/trueskill/tree/master) — N-group support works and is covered by invariants, but no reference values are asserted