## What changed?
Updated SAA ScheduleToClose timer validation to require an exact stamp
match. Legacy zero-stamp timers are now only accepted while the
activity’s current ScheduleToClose stamp is also zero.

## Why?
A stale pre-stamp ScheduleToClose timer could still time out an activity
after update-options had extended the timeout and emitted a newer
stamped timer.
Matching stamps exactly prevents old timer tasks from remaining valid
after the activity advances to a newer ScheduleToClose stamp.

## How did you test it?
- [X] built
- [X] run locally and tested manually
- [ ] covered by existing tests
- [ ] added new unit test(s)
- [X] added new functional test(s)

Implements Pause, Unpause, Reset, and UpdateActivityExecutionOptions
RPCs for standalone CHASM activities. Adds matching frontend and
history service handlers in chasm/lib/activity that dispatch to
either the workflow-activity path or the standalone-activity path
based on the presence of a workflow ID.

Also adds PAUSE_REQUESTED and RESET_REQUESTED state machine states
for standalone activities, the original_options snapshot for
restore-on-reset semantics, the activity-options merge helpers
(common/activityoptions), and the supporting proto schema changes
(start_request_id, sdk_name, sdk_version, etc.).

Squashed PRs:
  #9693  RPC boilerplate and code generation
  #9850  Implement UpdateActivityExecutionOptions
  #9851  Implement Pause/UnpauseActivityExecution for SAA
  #9852  Implement ResetActivityExecution for SAA
  #10001 Pause returns FailedPrecondition when already paused
  #10025 Validator function fixes
  #10265 Replace PauseState flag with PAUSE_REQUESTED state
  #10364 Add RESET_REQUESTED state to standalone activity
  #10745 Add support for updating start_delay via UpdateActivityOptions
  #10913 Preserve SAA retry backoff across unpause re-dispatch
  #10914 Fix SAA unpause for keep-paused reset
  #10917 Reject stale legacy SAA schedule-to-close timers
  #10920 Preserve NextRetryDelay across unrelated activity option updates
  #10921 Validate merged SAA retry policy updates
  #10923 Fix SAA reset attempt dispatch time reporting
  #11010 Use default retry policy when updating with nil
  #11020 Fix: de-duplicate pause even if activity is unpaused
  #11013 Fix: reject restore_original when a standalone activity has no original options snapshot
  #11032 Reject unsupported and empty update_mask paths in UpdateActivityExecutionOptions
  #11030 Fix: describe only provides heartbeat/failure when opted-in
  #11016 Preserve pending activity next retry delay
  #11068 Add SAA operator APIs to DC redirection whitelist
  #10954 Remove reset_heartbeats field in ResetActivityExecutionRequest
  #11087 Fix standalone activity heartbeat flag precedence
  #11117 Validation to reject negative activity jitter
  #11120 Fix bogus StartToCloseLatency for non-running standalone activities
  #11097 Fix task token invalidation after resetting an activity
  #11067 SAA bug fix: update start delay while paused
  #11123 SAA: cleanup