Avoid repeated numeric-list scans during trajectory serialization

[bradhilton]

Trajectory string interning checked whether a list contained only numeric values before consulting its graph memo, then returned without recording the list. Shared token/logprob-like vectors were therefore scanned repeatedly through each alias. Consult the existing per-traversal memo first and record numeric lists without copying or changing their values.

Validation:

• 30 compact-serialization tests pass, including a regression that reduces 64 scans to one, mutation between traversals, aliases, cycles, signed zero/NaN, and pickle/cloudpickle round trips.
• Actual cloudpickle.dumps of public synthetic trajectory-group callbacks produces byte-identical baseline/candidate payloads across five alternating repetitions. The alias-heavy case falls from 0.4518 s to 0.0080 s median CPU time (56.48×); independent equal vectors show no regression (0.4798 s to 0.4679 s). These are synthetic results; live alias frequency and end-to-end preparation gains are unmeasured.
• Ruff check/format and git diff --check pass. Independent source review passed.

The memo remains local to one traversal. No new API, global cache, tokenization behavior, or active-run source adoption.