Defer schedule catchup window default to server

[chaptersix]

What changed

• Make the default catch-up window nullable instead of assigning 60 seconds.
• Remove null policy fields during protobuf mapping.
• Preserve exact protobuf duration values when decoding server responses.
• Correct the public documentation.
• Add omission, exact-duration decoding, and server-backed one-year default coverage.

Why

The SDK was sending a historical 60-second default, preventing the server’s one-year default from taking effect. Its protobuf decoder also converted long fixed durations through a calendar diff, which changed the reported total seconds.

Validation

• GitHub Actions static analysis
• Unit coverage for exact protobuf duration decoding
• Server-backed schedule coverage confirms the 365-day default
• Tests were not run locally because PHP and Composer are unavailable.

Breaking changes

SchedulePolicies::$catchupWindow is nullable until the schedule is resolved by the server.

[chaptersix]

I'm not a PHP dev so apologies if this is slop. We just need to correct this docs and allow the server to select the proper default.

[chaptersix]

important thing is that the default should be 1 year. if this sdk wants to continue setting it, that's fine.