Add opt-in serial reconnect support

[CAOShurong]

Why

Board uploads, resets, and brief USB disconnects routinely invalidate a serial handle. TermScope previously converted the first read error into a fatal exit. Arduino's own upload flow closes and reopens its monitor; maintained alternatives confirm reconnect is expected, but either do not plot (tio, SimpleCom) or require a separate GUI (serial-monitor-rust).

What changed

• add opt-in --reconnect [SEC], preserving fail-fast behavior by default
• retry only the originally selected OS path and show reconnecting in the header
• never retry missing pyserial or invalid settings
• interrupt retry waits on stop and discard cross-session partial lines
• document identity/path, local-data, dependency, and physical-fixture boundaries
• release version 0.3.0

Verification

• red test observed first: constructor rejected reconnect and CLI rejected the flag
• 174 unit/integration tests pass
• Ruff lint/format, compileall, README regeneration check, build, and twine check pass
• clean wheel install: version/help, demo success, missing replay failure, fail-fast missing COM, and bounded reconnect failure all observed with expected exit codes
• clean sdist install and demo success observed
• Windows host had no present serial fixture; real USB unplug/reset behavior remains explicitly unverified pending independent Windows/macOS/Linux hardware reports