fix(RSpec split by examples): properly disable split by test examples on a single node to speed up tests

[ArturT]

Description

Fix for a bug introduced in the following PR when you run tests on a single CI node and use KNAPSACK_PRO_RSPEC_SPLIT_BY_TEST_EXAMPLES=true.

• Add KNAPSACK_PRO_SLOW_TEST_FILE_THRESHOLD to improve the RSpec split by examples feature with many skipped tests  #282

vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/slow_test_file_determiner.rb:29:in `read_from_json_report'
/home/betterment/for_business/impersonate/vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/adapters/base_adapter.rb:30:in `slow_test_file?'
/home/betterment/for_business/impersonate/vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/formatters/time_tracker.rb:123:in `rspec_split_by_test_example?'
/home/betterment/for_business/impersonate/vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/formatters/time_tracker.rb:117:in `path_for'
/home/betterment/for_business/impersonate/vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/formatters/time_tracker.rb:102:in `record_example'
/home/betterment/for_business/impersonate/vendor/bundle/ruby/3.2.0/gems/knapsack_pro-7.12.0/lib/knapsack_pro/formatters/time_tracker.rb:38:in `example_finished'

changes

• fix(RSpec split by examples): properly disable split by test examples on a single node to speed up tests

Checklist reminder

• You added the changes to the UNRELEASED section of the CHANGELOG.md, including the needed bump (ie, patch, minor, major)
• You follow the architecture outlined below for RSpec in Queue Mode, which is a work in progress (feel free to propose changes):
  • Pure: lib/knapsack_pro/pure/queue/rspec_pure.rb contains pure functions that are unit tested.
  • Extension: lib/knapsack_pro/extensions/rspec_extension.rb encapsulates calls to RSpec internals and is integration and e2e tested.
  • Runner: lib/knapsack_pro/runners/queue/rspec_runner.rb invokes the pure code and the extension to produce side effects, which are integration and e2e tested.