Extracts ScopeBatcher from PR #5431, the in-progress symbol database
upload work. The class batches Scope objects produced by the extractor
and triggers the Uploader (#5670) at appropriate times.

Two upload triggers:
- Size-based: 400 scopes (MAX_SCOPES, matches Java/Python tracers)
- Time-based: 1s of inactivity (debounce timer, not periodic)

Plus deduplication of already-uploaded module names, a 10,000-file
limit to bound memory in heavily-modularized apps, and Mutex-protected
state for concurrent add_scope calls.

Timer implementation is a single long-lived thread waiting on a
ConditionVariable with timeout. Each add_scope signals the CV to reset
the deadline; when the timeout expires without a signal, the timer
fires and flushes the batch. Avoids the thread-per-add_scope cost of
the earlier design.

The Component class (still in #5431) wires ScopeBatcher between
Extractor and Uploader. Forward-references in scope.rb, uploader.rb,
and extractor.rb that mention ScopeBatcher become accurate with this
PR.

Co-Authored-By: Claude <[email protected]>

CRITICAL fixes from di-pr-review on this PR:

1. Add telemetry reporting in all rescue blocks. Per the symdb error
   handling rule, every rescue must log and report telemetry. Added
   `telemetry: nil` constructor parameter and `@telemetry&.report(e,
   description: '...')` in add_scope, timer_loop, and perform_upload
   rescues. Description strings are constants (no unbounded
   interpolation); exception class/message stay in logger.debug only.

2. RBS: prefix all stdlib classes with `::`. Integer, Float, Proc,
   Array, Mutex, Thread, ConditionVariable, Set, String now resolve
   via global namespace, preventing accidental resolution to a class
   in the current module's namespace.

3. Test coverage for the three rescue blocks: add_scope (broken
   uploaded_modules Set), perform_upload (uploader raises), and
   timer_loop (broken @scopes during debounce). Each test verifies
   logging content AND telemetry.report is called with the right
   description, AND that the exception does not propagate.

Tier 2 fixes:

4. Race condition in shutdown/reset. Both methods set @timer_thread =
   nil outside the mutex, allowing a concurrent add_scope to create a
   new timer thread that gets orphaned. Capture the thread reference
   inside the mutex, nil the field inside the mutex, then join the
   captured local outside the mutex.

5. Move `reset` to private. Was documented `@api private` but exposed
   as a public method. Tests now use `send(:reset)`.

6. Drop the three `# steep:ignore:start`/`:end` blocks. They were
   masking type errors that disappear once `scopes_to_upload` is
   declared as `::Array[Scope]?` via `# @type var` annotations.

Verification:
- bundle exec steep check lib/datadog/symbol_database/scope_batcher.rb
  → No type error detected.
- bundle exec rake standard → clean
- bundle exec rspec spec/datadog/symbol_database/scope_batcher_spec.rb
  → 29 examples, 0 failures (3 new rescue-coverage tests).

Co-Authored-By: Claude <[email protected]>

Address review comment from Codex: @file_count was incremented before
the dedup check, so repeated calls for an already-uploaded scope still
consumed the MAX_FILES budget. In a re-extraction scenario where the
same scopes are offered again (e.g., a Rails reload), 10,000 duplicate
offerings would exhaust the budget and cause subsequent unique scopes
to be dropped at the limit — contrary to the documented "Maximum
unique files" intent.

Move @file_count += 1 to after the dedup check, so only accepted
unique scopes consume the budget. Add a test that offers the same
scope MAX_FILES + 1 times then verifies a subsequent unique scope is
still accepted (the budget was not exhausted by duplicates).

- Fixed in lib/datadog/symbol_database/scope_batcher.rb:73-95
- Test added in spec/datadog/symbol_database/scope_batcher_spec.rb

Verification:
- bundle exec rspec spec/datadog/symbol_database/scope_batcher_spec.rb
  → 30 examples, 0 failures
- bundle exec steep check lib/datadog/symbol_database/scope_batcher.rb
  → No type error detected.
- bundle exec rake standard → clean

Co-Authored-By: Claude <[email protected]>