boca: Fix the parser for startTime and duration.

For startTime seconds the type is int64, it's serialized as string.
StartTime nanos type is int32, serialized as int. Same for Duration.

Test: unit tested.
Bug: b: 371086378
Change-Id: If02ba6a6349c753641ebdee6a35dc67a01d7dc4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5906735
Commit-Queue: April Zhou <aprilzhou@google.com>
Reviewed-by: Benjamin Zielinski <bzielinski@google.com>
Cr-Commit-Position: refs/heads/main@{#1363773}