Remove `DELETE_FAST` bytecode instruction

DELETE_FAST has two uses:

1. delete var where var is a local variable
2. Cleaning up at the end of a named exception block.

A local variable can be deleted with the sequence PUSH_NULL; STORE_FAST var.

Deleting a local variable

Instead of DELETE_FAST n we can emit LOAD_FAST n; POP_TOP n; PUSH_NULL; STORE_FAST n which the bytecode optimizer will reduce to PUSH_NULL; STORE_FAST n in most cases.

Cleaning up at the end of a named exception block.

We currently emit the sequence: LOAD_CONST None; STORE_FAST n; DELETE_FAST n
which can be replaced with PUSH_NULL; STORE_FAST n

This case is far more common than explicitly deleting a local variable, so we can reduce code size as well as freeing up an opcode.

See https://github.com/faster-cpython/ideas/issues/490

Linked PRs

• gh-145983

Start by tracing the compiler entry points that emit DELETE_FAST for local deletion and named-exception cleanup. Compare their bytecode output with the proposed PUSH_NULL; STORE_FAST sequences, then verify that DELETE_FAST is no longer emitted and existing bytecode tests still pass; the issue references linked PR gh-145983.