refactor: unify convergence defaults, validate builders, clear dead code

Convergence configuration had two disagreeing sources of truth and one
misleading report:

- `EpsilonOrMax::default()` capped at 10 iterations while
  `ConvergenceOptions::default()` allowed 30, and which applied depended on
  whether inference went through `run_chain` or a `Schedule`. The schedule
  default now derives from `ConvergenceOptions`.
- A graph with no iterating factors reported `converged: false` with an
  infinite step, despite being at its fixed point after the setup pass. It
  now reports converged with a zero step.
- `TimeSlice::iterate_to_convergence` hard-coded an epsilon and a
  20-iteration cap matching neither. It reads `self.convergence` and is
  scoped to `#[cfg(test)]`, which is all it was ever used by.

`HistoryBuilder::p_draw` and `::convergence` now validate their arguments
like `score_sigma` already did, instead of accepting a negative `p_draw` or
an `alpha` of zero — the latter leaves every EP update unapplied, so
inference silently returns the priors.

Removing the `#[allow(dead_code)]` masks let the compiler report what they
were hiding: four `OwnedGame` fields that were stored and never read, two
`ColorGroups` helpers and three `SkillStore` helpers used only by tests, and
`iterate_to_convergence` above. Test-only items are now `#[cfg(test)]` and
the unread fields are gone.

Also exported `HistoryBuilder`, which was public but unreachable — callers
could chain `History::builder()` but could not name the type — and added
`Rating::{prior, beta, drift}` and `Index::get`, so handles the API hands
out can be read back.

Two goldens moved, both convergence residuals rather than exact values:
`iterate_to_convergence` now runs to 30 iterations instead of 20, landing
nearer the symmetric truth of 25.0.

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

src/game.rs

@@ -88,16 +88,12 @@ impl Default for GameOptions {
 /// Owned variant of `Game` returned by public constructors.
 ///
 /// Unlike `Game<'a, T, D>` (which borrows its result/weights slices from
-/// History's internal state), `OwnedGame<T, D>` owns its inputs so it can
-/// be returned freely from public constructors.
+/// History's internal state), `OwnedGame<T, D>` owns the team ratings, so it
+/// can be returned freely from public constructors. The inference inputs
+/// themselves are not retained — nothing reads them back.
 #[derive(Debug)]
-#[allow(dead_code)]
 pub struct OwnedGame<T: Time, D: Drift<T>> {
     teams: Vec<Vec<Rating<T, D>>>,
-    result: Vec<f64>,
-    weights: Vec<Vec<f64>>,
-    p_draw: f64,
-    pub(crate) convergence: crate::ConvergenceOptions,
     pub(crate) likelihoods: Vec<Vec<Gaussian>>,
     pub(crate) log_evidence: f64,
 }
@@ -119,16 +115,10 @@ impl<T: Time, D: Drift<T>> OwnedGame<T, D> {
             convergence,
             &mut arena,
         );
-        let likelihoods = g.likelihoods;
-        let log_evidence = g.log_evidence;
         Self {
             teams,
-            result,
-            weights,
-            p_draw,
-            convergence,
-            likelihoods,
-            log_evidence,
+            likelihoods: g.likelihoods,
+            log_evidence: g.log_evidence,
         }
     }
 
@@ -148,16 +138,10 @@ impl<T: Time, D: Drift<T>> OwnedGame<T, D> {
             convergence,
             &mut arena,
         );
-        let likelihoods = g.likelihoods;
-        let log_evidence = g.log_evidence;
         Self {
             teams,
-            result: scores,
-            weights,
-            p_draw: 0.0,
-            convergence,
-            likelihoods,
-            log_evidence,
+            likelihoods: g.likelihoods,
+            log_evidence: g.log_evidence,
         }
     }