Add property-based coverage for inline date-sequence matching

[pandalump]

Summary

Add focused property-based coverage for inline date-sequence matching in a separate pull request.

The initial property tests were removed from PR #395 because date-sequence matching is outside the scope of issues #364, #372, #374, #388, and #397.

Acceptance criteria

• Cover valid prefixed date sequences across generated separators and tokens.
• Cover empty and incomplete sequences without changing production matching behaviour.
• Keep the work isolated from PR Harden wrapping and table reflow (#388) (#374) (#372) (#364) #395.

[coderabbitai]

🔗 Related PRs

#343 - Preserve fenced code block contents during wrapping (#329) [closed]
#350 - Treat date-like sequences as atomic inline fragments (#346) [closed]
#356 - Keep escaped backtick code spans atomic (#354) [closed]
leynos/rstest-bdd#583 - Restore the coverage ratchet (#582) [merged]
#395 - Harden wrapping and table reflow (#388) (#374) (#372) (#364) [open]

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