Implement Phase 2a Bracket-Form Expose Filter Evaluation

[Malcolmnixon]

This pull request completes Phase 2a of the expose bracket-filter feature in the SysML2Tools core, enabling evaluation of bracketed expose <path>::**[<expr>] filter forms. The implementation reuses the existing Phase 1 parser/evaluator, introduces a paired data model for expose entries, and ensures that bracket filters are correctly matched to their intended targets. The documentation is updated throughout to reflect these enhancements, and requirements traceability is strengthened. Deferred work for more advanced filter constructs and usage-level metadata is explicitly documented.

Bracketed expose filter evaluation (Phase 2a):

• The bracketed expose <path>::**[<expr>] filter form is now parsed and evaluated, narrowing the exposed scope to only the definitions matched by the filter. Failures to parse or evaluate degrade gracefully to whole-subtree inclusion, with warnings only on actual failures. [1] [2] [3] [4] [5] [6]
• The data model for expose entries is refactored: instead of parallel lists, a single ExposeMembers list pairs each path with its bracket filter expression, ensuring correct association. [1] [2] [3] [4]

Scope resolution and error handling:

• ExposeScopeResolver now returns an ExposedScope record with PrefixSubjects, ExplicitMembers (for matched definitions), and Failures (for failed bracket filters). The resolution logic is enhanced to pair resolved edges with their originating ExposeMember via a forward-scanning heuristic. [1] [2] [3]
• Error handling is robust: failures in bracket filter parsing/evaluation are recorded and surfaced as warnings, never as exceptions or rendering failures. [1] [2]

Documentation and requirements traceability:

• All relevant documentation is updated to describe the new behavior, data model, and error handling. Requirements traceability sections are added or expanded to map features to implementation units. [1] [2]

Deferred work:

• Advanced filter constructs (e.g., istype, arithmetic, conditionals) and usage-level metadata filtering remain deferred, as no real-world need is observed. This is clearly documented for future reference.

These changes collectively make bracketed expose filters fully functional, robust, and well-documented, while leaving a clear path for future enhancements.