feat(game): plumb ConvergenceOptions through to run_chain

Game and OwnedGame gain a convergence: ConvergenceOptions field set at
construction. Game::{ranked,scored} forward options.convergence into
OwnedGame::{new,new_scored} (previously dropped on the floor).
{ranked,scored}_with_arena take it as a parameter. run_chain reads
self.convergence.{epsilon, max_iter, alpha} instead of hardcoded
1e-6 / 10 / undamped. DiffFactor::propagate gains an alpha parameter
and dispatches into Trunc/MarginFactor::propagate_with_alpha.

In-tree callsites in src/time_slice.rs and src/history.rs pass
ConvergenceOptions::default(). Pre-existing T2 fallout in tests,
benches, and the atp example (struct literals missing the new alpha
field) is fixed by adding alpha: 1.0 so the workspace builds clean.
Default alpha is 1.0, so all 96 lib + 27 integration test goldens
remain bit-equal.

tests/api_shape.rs

@@ -15,6 +15,7 @@ fn add_events_bulk_via_iter() {
         .convergence(ConvergenceOptions {
             max_iter: 30,
             epsilon: 1e-6,
+            alpha: 1.0,
         })
         .build();
 

tests/determinism.rs

@@ -16,6 +16,7 @@ fn build_and_converge(seed: u64) -> Vec<(i64, trueskill_tt::Gaussian)> {
         .convergence(ConvergenceOptions {
             max_iter: 30,
             epsilon: 1e-6,
+            alpha: 1.0,
         })
         .build();
 

tests/record_winner.rs

@@ -10,6 +10,7 @@ fn record_winner_builds_history() {
         .convergence(ConvergenceOptions {
             max_iter: 30,
             epsilon: 1e-6,
+            alpha: 1.0,
         })
         .build();