fix: Equal, Map lookup, and ContainsSeq correctness improvements

[freeformz]

Summary

• Equal optimization: Remove redundant Subset(b, a) call — when cardinalities are verified equal, a single Subset(a, b) check is sufficient to prove set equality
• Map.Add/Remove optimization: Inline map key lookup (_, ok := s.set[m]) instead of calling the Contains method, eliminating a redundant method call per operation
• ContainsSeq vacuous truth: Return true for empty sequences, matching mathematical convention (universal quantification over an empty domain is vacuously true) and consistent with ContainsAll() behavior
• CLAUDE.md conventions: Document project patterns (zero-value style, tests-as-spec, mathematical correctness, conventional commits)

Test plan

• All existing tests pass with -race
• No gopls diagnostics
• ContainsSeq behavior now consistent with ContainsAll for empty input

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR tightens correctness and reduces overhead in core set helper functions, while documenting repository conventions in CLAUDE.md.

Changes:

• Simplifies Equal to a single Subset(a, b) check after verifying equal cardinalities.
• Makes ContainsSeq return true for an empty sequence (vacuous truth), aligning with ContainsAll.
• Inlines map key lookups in Map.Add/Remove to avoid a redundant Contains call; documents project conventions in CLAUDE.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
set.go	Optimizes Equal and updates ContainsSeq empty-sequence semantics.
map.go	Inlines map lookups in Add/Remove to avoid extra method calls.
CLAUDE.md	Adds documented conventions (zero-value style, tests-as-spec, math semantics, conventional commits).

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

map.go:66

• Add writes to s.set without ensuring the map is initialized. If a Map is used via its zero value (e.g., var s Map[int]), Add will panic on s.set[m] = .... Consider initializing s.set when nil (similar to Clear) before doing lookups/writes.

func (s *Map[M]) Add(m M) bool {
	if _, ok := s.set[m]; ok {
		return false
	}
	s.set[m] = struct{}{}
	return true

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