Align LRU cache keys and callback controls - #9681

Summary

• Match LRU constructor keyword names and conversion order, scalar-key distinctions, and copy-method arity through shared binders and converters.
• Move bounded hits without replacing stored keys or repeating equality callbacks.
• Keep cache clearing, recursive insertion and eviction consistent under reentrant equality and finalizers.
• Add two narrow dictionary operations using existing entry revalidation, leaving unrelated get/pop callers unchanged.

The helper changes address stale reads or removals when equality clears and repopulates a dictionary position. Failed insertion releases the newly computed result before the evicted key/result, matching CPython.

Reference: CPython 3.15.0 LRU implementation.

Validation

• Independent source review and 13 bounded CPython 3.15 reference groups cover conversion, scalar keys, recursion, equality reentry, eviction and finalizer order.
• Formatting and whitespace checks passed.
• Final focused VM, host-env and stdlib check and strict Clippy with rustpython-stdlib/threading passed after removing the obsolete deletion wrapper and a redundant clone. Normal repository hooks passed.
• RustPython runtime, full workspace/C-API suites and cross-platform execution were not run. No test, Lib, workflow or marker edits.

Composition with #9679 requires reconciling the shared import hunk to retain both ArgIntoBool and Callee; the behavioral sections are separate.

AI assistance: OpenAI Codex performed source comparison, implementation, reference probes and independent source review; model version was not exposed.