Cache @Computed/@Derived method descriptors in Record.StaticAnalysis

[jtnelson]

Summary

Record.$computed() (Record.java:2377) and $derived()
(Record.java:2428) memoize their results per instance, but the work
they cache -- scanning the full method hierarchy
(getAllNonOverriddenDefaultInterfaceMethods + getAllDeclaredMethods)
and probing each method for @Computed / @Derived -- produces a
class-level fact. A bulk load of N records of the same class pays N
identical reflective scans.

Implementation Plan

1. Move descriptor discovery (which methods are @Computed/@derived, their
   resolved keys, and isDefault) into the existing class-keyed
   Record.StaticAnalysis inner class, computed once per class.
2. Per instance, only bind the suppliers (computed) / evaluate the values
   (derived) from the cached descriptors.

Acceptance Criteria

• The method hierarchy is scanned at most once per class, not per
  instance.
• Computed suppliers still bind to the instance; derived values still
  evaluate per instance.
• Existing computed/derived tests pass.

Effort

Small-Medium