feat(api): typed add_events(iter); generify internal path over T

Public API gains:

  History::add_events<I: IntoIterator<Item = Event<T, K>>>(events)
      -> Result<(), InferenceError>

which accepts the typed Event<T, K> shape added in Task 10. Ranks
from Outcome::Ranked are mapped to the legacy "higher f64 = better"
results internally.

add_events_with_prior now takes Vec<T> for times (was Vec<i64>),
generifying the whole internal path over T in a single fully-generic
impl<T: Time, D: Drift<T>, O: Observer<T>, K> block. The i64-specific
block is gone; record_winner/record_draw are now generic over T.

add_events_with_prior stays pub (not pub(crate)) because the ATP
example calls it directly with pre-built Index-based composition;
the new typed add_events is the primary public API going forward.

In-crate tests updated to call add_events_with_prior with an empty
HashMap. tests/api_shape.rs added with 3 integration tests covering
bulk ingest, draw, and mismatched-outcome error.

Part of T2 of docs/superpowers/specs/2026-04-23-trueskill-engine-redesign-design.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/atp.rs

@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+
 use plotters::prelude::*;
 use time::{Date, Month};
 use trueskill_tt::{History, KeyTable};
@@ -40,7 +42,7 @@ fn main() {
 
     let mut hist = History::builder().sigma(1.6).gamma(0.036).build();
 
-    hist.add_events(composition, results, times, vec![])
+    hist.add_events_with_prior(composition, results, times, vec![], HashMap::new())
         .unwrap();
     hist.convergence(10, 0.01, true);