add core static value member support

[KurodaKayn]

Summary

• Add the core static value member path for named types.
• This introduces NewStaticMember so package-level const/var objects can be associated with a named type and resolved through normal CodeBuilder.Member handling on TypeType receivers.
• Part of support static value members for named types #637

Changes

• Add NewStaticMember for registering static const/var members on named types.
• Resolve registered static value members from cb.Typ(T).MemberVal(...).
• Resolve registered static var members from cb.Typ(T).MemberRef(...) so assignable operations like inc/dec work.
• Keep static methods and static value members in the same member namespace by rejecting collisions.
• Normalize generic instantiated named types to Origin() for static member lookup, so Box[int].name can resolve members registered on Box[T].

Testing

• go test -run 'TestStaticMember|TestStaticMethod' ./...
• go test ./...
• git diff --check

[gemini-code-assist]

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[fennoai]

Summary

The PR introduces a clean, mutex-protected registry for associating const/var objects with named types. Generic-type origin normalization via staticMemberOrigin is handled consistently, and the integration into Member() correctly places static lookup ahead of regular method/field resolution without breaking the existing isType && kind != MemberMethod guard.

Three inline findings cover misleading panic messages and dead code. Two non-inline findings cover a missing symmetric test and the global registry lifetime.

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Missing test — NewStaticMethod after NewStaticMember conflict (xgo_test.go)

The new guard added to NewStaticMethod (if lookupStaticMember(typ, name) != nil { ... }) has no direct test coverage. TestStaticMemberMethodConflict exercises the reverse direction only (static member after static method). A symmetric test would prevent regressions on this new guard.

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Global registry lifetime (func_ext.go, staticMemberValues)

Unlike NewStaticMethod, which stores entries directly on the *types.Named via the Go type system (and is collected when the type is GC'd), staticMemberValues is a process-global map that never evicts entries. In long-lived processes that build many packages (e.g. a language server or batch compile server), this retains *types.Named pointers and their types.Object values indefinitely. Consider scoping the registry to a Package/builder instance, or documenting the lifetime trade-off with a comment on the global.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.70%. Comparing base (4e08570) to head (823891a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #638      +/-   ##
==========================================
+ Coverage   93.63%   93.70%   +0.06%     
==========================================
  Files          29       29              
  Lines        7167     7240      +73     
==========================================
+ Hits         6711     6784      +73     
  Misses        388      388              
  Partials       68       68              

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