[albertedwardson]

closes #140328

intern_constants() previously only interned string constants when should_intern_string() returned true, leaving equal strings duplicated even if an interned instance already existed. This change first checks the global and per-interpreter interned string tables and reuses an existing interned string when available. This applies only to string constants that come from the codeobjects; dynamically created strings are unaffected and are still created as new objects.

This makes string interning behavior more consistent: once a string is interned, subsequent equal constants can reuse the canonical object. It may slightly reduce memory usage and improves interaction with sys.intern().

The change adds a small lookup cost when loading code objects, which may affect eval(), exec(), modules loading and similar operations.

I haven't run pyperformance yet, but I plan to provide a benchmark run once I have access to an appropriate runner. Given the limited scope of the change, I expect both the performance impact and memory savings to be relatively small but measurable.

• Issue: Use interned versions of string constants if they're already present #140328