Render tz-aware times as local times without an offset

[Master-Norna]

Summary

item() and Time._new built the raw literal with time.isoformat(), which includes the UTC offset for tz-aware values - e.g. 07:32:00+02:00. TOML local times have no offset or timezone (the spec's examples are plain 07:32:00), and this library's own parser rejects the offset, so the serialized document was invalid and could not be read back:

i = item(time(7, 32, tzinfo=timezone(timedelta(hours=2))))
i.as_string()   # before: '07:32:00+02:00'  (rejected by tomlkit.parse)
                # after:  '07:32:00'

Render from hour/minute/second/microsecond only. Naive times are byte-for-byte unchanged.

Agent Drafting Metadata

• Agent: Claude (Anthropic)
• Model: Claude Opus
• Notes: Agent assisted with investigation and drafting; the fix, tests and verification were reviewed by the submitter. Full suite passes (1059 passed).

[frostming]

Please resolve the conflict

[Master-Norna]

Rebased onto the latest master — the conflict was with the fold argument in #620, which now coexists with the _format_time rendering. Full suite passes locally (1064) and CI is green. Thanks!