gh-157407: Reduce code size of ast and unicodeobject

[methane]

This pull request refactors and optimizes the initialization and cleanup code for AST annotations and global static strings, focusing on reducing .text segment size.
This change reduces the size of Python's .text segment by approximately 1%, or about 60 KiB.

The main changes involve switching to offset-based iteration for both AST type cleanup and string initialization, and consolidating annotation logic to avoid code duplication.

Disclosure of the use of AI:

• This change was selected and refined by me from a set of code-size reduction changes generated by Codex.
• The description above was edited by me based on Copilot's "Generate Summary."
• This text was translated into English by ChatGPT from the Japanese text I wrote.

• Issue: Reduce some code sizes #157407

[picnixz]

Can you create an issue for such changes please? just for tracking purposes

[methane]

This pr reduces:

• add_ast_annotations: 48K bytes
• _PyAST_Fini : 13K bytes
• _PyUnicode_InitGlobalObjects : 10K bytes

[hugovk]

Looks like this caused test_peg_generator to fail on a number of AMD64 Windows (tier 1) buildbots:

Python-ast.c(835): error C2099: initializer is not a constant

For example: https://buildbot.python.org/#/builders/1620/builds/4536