💥 feat(sdk): enforce some activity to close timeout is set

[chris-olszewski]

What was changed

• Move to a builder for ActivityOptions
• Combine schedule_to_close_timeout and start_to_close_timeout into a combined field of close_timeouts: ActivityCloseTimeouts to enforce that some timeout to close is set.

Aside from the vanilla builder we add a few methods to help with ergonomics by letting them skip importing the new enum:

• ActivityOptions::schedule_to_close_timeout/ActivityOptions::start_to_close_timeout: Directly construct activity options with just this timeout set
• ActivityOptions::with_schedule_to_close_timeout/ActivityOptions::with_start_to_close_timeout: Start an options builder with one of these timeouts set
  There is no both variant for these since it would take 2 Duration objects and there isn't a clear way to indicate which one is for which timeout without a struct, which we already have this with the enum.

Why?

Collapsing the close timeouts allows us to enforce that all activities must have a timeout to close.

I ended up combining this with moving ActivityOptions to a builder as the close timeout change was invasive enough and at the end of the day I wanted to see the end state of how we want users to construct these options.

Alternatives Considered

There is a nice design where we continue to expose the activity timeout setting only via the builder with .start_to_close_timeout and schedule_to_close_timeout setters that both flow into a single required field.
elastio/bon#149

Checklist

1. Closes N/A

2. How was this tested:
   Migrated existing tests/examples to use new activity options API

3. Any docs updates needed?
   README was updated

[Sushisource]

Nice! This is a big improvement.