fix(spec): parse commit duration options and align their defaults with Java

[jackylee-ch]

commit.timeout, commit.min-retry-wait and commit.max-retry-wait are
durationType() in Java, but Rust parsed bare milliseconds only: commit.timeout = '2 min' failed to parse and silently fell back to the default, so a plausible
configuration was accepted and ignored. Two of the defaults also diverged —
min-retry-wait was 1000ms against Java's 10ms, and the timeout was 120000ms where
Java leaves it unset and lets commit.max-retries bound the loop alone. Those
compound: Rust slept ~75s across its retry budget where Java sleeps ~10s, and could
then abandon the commit on wall clock with "there may exist commit conflicts between
multiple jobs" while Java was still retrying.

Fix: add parse_duration_millis, mirroring TimeUtils.parseDuration and shaped
like the existing parse_memory_size — every Java unit label, case-insensitive,
bare number as millis, None on overflow. Align the two defaults, using u64::MAX
as the unbounded sentinel; the value is only ever compared against elapsed time, so
no arithmetic can overflow.

Bare-millisecond values keep working, since Java reads an empty unit label as millis too.