[kaiks]

Summary

• keep one execution map when test workers generate it at the same time
• lock map initialization, writes, and reads
• merge duplicate example entries by taking the union of their dependencies
• preserve the original replace behavior for nonparallel map generation
• share parallel-runner environment detection with the evaluation code

Problem

Each map generator worker cleared the shared YAML file during RSpec startup. A later worker therefore removed data written by an earlier worker. Concurrent YAML appends could also overlap.

The feature test runs two Kaia-style workers concurrently. One worker runs the Class1 spec and the other runs the Class2 spec. The final map must contain data from both workers.

Verification

• bundle exec rspec spec features (312 examples, 0 failures on Ruby 4.0)
• bundle exec rubocop
• bundle exec yard --fail-on-warning
• bundle exec rake build
• focused storage, generator, runner configuration, and parallel feature tests on Ruby 3.2 (48 examples, 0 failures)

This PR is stacked on #1, which fixes parallel prediction evaluation.