Align constant-table and nested code-object emission order in large modules

[youknowone]

Summary

Some large remaining diffs are dominated by module-level constant layout and nested code-object ordering, not
only by local CFG issues.

Evidence

The clearest cases are:

• Lib/test/test_ast/snippets.py: 1 code object, 4216 instruction diffs
• Lib/test/test_dis.py: module-level drift plus smaller function-level drift

Representative mismatches include:

• CPython loading a large constant blob or nested code object from co_consts
• RustPython loading a different constant earlier, or emitting nested code objects in a different order
• large EXTENDED_ARG / constant-index layout divergence caused by different constant ordering

Expected direction

RustPython should match CPython’s ordering for:

• nested code object insertion
• large constant materialization
• constant-table population where it affects emitted bytecode

Likely implementation areas

• crates/codegen/src/compile.rs
• code-object construction / constant collection order

Done when

test_ast/snippets.py and the module-level part of test_dis.py stop diverging as a single giant constant-
layout mismatch and instead match CPython’s constant ordering and nested code-object structure.