Add auto-resume feature and bump version (0.3.31)

[aliroberts]

Summary

Wraps the optimization loop so that transient network failures (ConnectionError, ReadTimeout, HTTP 502/503/504) auto-resume the run instead of bailing out. Enabled by
default, with CLI overrides. Non-transient failures (auth, 4xx, insufficient credits, Ctrl-C) still propagate unchanged. Bumps version to 0.3.31.

CLI

weco run ... [--no-auto-resume] [--auto-resume-max-attempts N]
weco resume ... [--no-auto-resume] [--auto-resume-max-attempts N]

Defaults: enabled, 5 attempts, 5s initial backoff, exponential (×2) capped at 60s.

Implementation notes

• _run_loop_with_auto_resume in weco/optimizer.py drives run_optimization_loop as a closure. On transient exit it sleeps with exponential backoff, calls
  WecoClient.resume_run silently (_silent_resume), and re-enters the loop with start_step = result.final_step. Non-transient results return verbatim.
• run_optimization_loop now catches ConnectionError / ReadTimeout explicitly and tags them transient_network_error instead of landing in the generic unknown bucket.
  HTTPError branch is unchanged; transient classification uses reason ∈ {transient_network_error, http_502, http_503, http_504}.
• _silent_resume failures retry in-place (don't re-invoke the loop), so when the backend is unreachable we don't spin in get_execution_tasks for 10 minutes between resume
  attempts.
• New UI events on_reconnecting(attempt, max, backoff_s) / on_reconnected() on the OptimizationUI protocol. Rich UI adds a reconnecting status (📡, yellow) with
  attempt/backoff in the status row; plain UI prints [RECONNECTING] / [RECONNECTED] lines. Exhaustion routes through on_error so it lands in the prominent Error row.
• AutoResumePolicy dataclass carries the overrides; both optimize() and resume_optimization() accept one and default to AutoResumePolicy() when absent.

Tests

• tests/test_auto_resume.py: 21 tests covering classification across 12 reasons, happy path, transient-then-success, exhaustion, disabled policy, _silent_resume failure
  retries without re-invoking the loop, exponential backoff with cap, and event payload shape.