fix(plot): add docstrings to nested _ev / _trial_of (interrogate 100%)

CI interrogate requires 100% docstring coverage; the two nested helpers in
plot_session_in_time_plotly were missing docstrings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hanhou

src/aind_dynamic_foraging_basic_analysis/plot/plot_foraging_session_plotly.py

@@ -543,6 +543,7 @@ def _to_curve(v):
             boundaries.append(cum)
 
         def _ev(name, _ev=ev_s, _off=off):
+            """Timestamps of events named ``name`` in this session, shifted by ``_off``."""
             return _ev.loc[_ev["event"] == name, "timestamps"].to_numpy() + _off
 
         tr_s = None
@@ -559,6 +560,7 @@ def _ev(name, _ev=ev_s, _off=off):
             first_gc = gc.min()
 
         def _trial_of(times, _gc=gc, _n=n_tr):
+            """Per-session trial number for each time (# go cues at/before it)."""
             if _n == 0:
                 return np.zeros(len(times), dtype=int)
             return np.searchsorted(_gc, np.asarray(times), side="right")