Fix cycle tags with variable arguments

[efegokdemir]

Summary

• Build unnamed cycle keys from lookup paths instead of lookup object identity, so repeated tags with the same variable expressions share and advance their cycle counter.
• Add regression coverage for the reported undefined-variable case and for a defined first value.
• Update the existing lookup-cycle expectation to reflect the shared-counter behavior requested in the issue.

This intentionally changes the prior per-tag counter behavior for identical lookup expressions; repeated unnamed cycle tags now behave consistently with literal cycles.

Fixes #2123

Tests

• PATH=/opt/homebrew/opt/ruby/bin:$PATH BUNDLE_WITHOUT=spec bundle exec ruby -Itest test/integration/tags/cycle_tag_test.rb — 13 runs, 57 assertions passed.
• PATH=/opt/homebrew/opt/ruby/bin:$PATH bundle exec rake — all unit/integration modes and RuboCop passed.
• git diff --check — passed.