feat(flags): add semver targeting to local evaluation

[dmarticus]

Summary

• Add 9 semver operators for local flag evaluation: semver_eq, semver_neq, semver_gt, semver_gte, semver_lt, semver_lte, semver_tilde, semver_caret, semver_wildcard
• Implement parse_semver function that handles v-prefix, whitespace, pre-release suffixes, partial versions (e.g., "1.2" → "1.2.0"), and 4-part versions
• Add bounds calculation for range operators following npm/semver conventions:
  • Tilde (~1.2.3): >=1.2.3 <1.3.0
  • Caret (^1.2.3): >=1.2.3 <2.0.0 (with special handling for 0.x versions)
  • Wildcard (1.2.*): >=1.2.0 <1.3.0

This enables targeting users by app/SDK version without network calls, matching the behavior in:

• PostHog server: feat(flags): support semver comparisons in user_blast_radius posthog#44596
• Python SDK: feat: add semver targeting support to local flag evaluation posthog-python#447

Test plan

• Added 19 comprehensive test cases covering:
  • All 6 basic comparison operators (eq, neq, gt, gte, lt, lte)
  • All 3 range operators (tilde, caret, wildcard) with boundary conditions
  • Edge cases: v-prefix, pre-release suffixes, whitespace, leading zeros
  • Partial versions (1.2 → 1.2.0, 1 → 1.0.0)
  • 4-part versions (1.2.3.4 → 1.2.3)
  • Invalid input handling (raises InconclusiveMatchError)
  • Missing/null property values
• Run bundle exec rspec spec/posthog/feature_flag_spec.rb — all 70 tests pass