docs: complete the public API documentation contract

Closes the last open item in #25. `cargo clippy -W missing_errors_doc
-W missing_panics_doc -W must_use_candidate -W doc_markdown` went from 56
warnings to zero.

The 13 hand-written sections name the actual variants each function returns
rather than gesturing at "an error". Establishing that meant reading the error
paths — `Game::ranked` alone returns four distinct variants, and `record_draw`
can hit TieWithoutDrawProbability where `record_winner` provably cannot, since
a two-team decisive outcome has nothing to tie. Documenting those as
interchangeable would have been worse than leaving them undocumented, because
a reader would trust it.

Two existing doc comments already described panics in prose but not under a
`# Panics` heading, so neither rustdoc nor clippy surfaced them:
`Outcome::winner` and `EventBuilder::weights`. Both now carry the heading, and
`Outcome::winner` gained the note that it ties every loser, so `n >= 3` needs a
positive p_draw — the crate's easiest error to hit by accident.

The 43 mechanical fixes (31 `#[must_use]` on pure accessors, 11 missing
backticks) were applied with `cargo clippy --fix`. `#[must_use]` on Gaussian's
arithmetic and on `posteriors()` matters: discarding those results is always a
bug, and until now nothing said so.

Also documented why `[profile.release] debug = true` exists — cargo-flamegraph
needs the symbols, and library profile settings are ignored downstream, so it
reads as an oversight without the note.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T5SYDExxL4vZgvunrcNSMc

src/event_builder.rs

@@ -50,8 +50,10 @@ where
 
     /// Set per-member weights for the most recently added team.
     ///
-    /// Panics in debug builds if called before `.team(...)` or if the length
-    /// doesn't match the team's member count.
+    /// # Panics
+    ///
+    /// Panics if called before any `.team(...)`. In debug builds, also panics
+    /// if the number of weights does not match the team's member count.
     pub fn weights<I: IntoIterator<Item = f64>>(mut self, weights: I) -> Self {
         let idx = self
             .current_team_idx
@@ -103,6 +105,10 @@ where
     }
 
     /// Commit the event to the history.
+    ///
+    /// # Errors
+    ///
+    /// Forwards to [`History::add_events`] and returns its errors.
     pub fn commit(self) -> Result<(), InferenceError> {
         self.history.add_events(std::iter::once(self.event))
     }