[build] Freeze startup encoding modules into CPython binary

[ppenna]

Summary

Freeze the five encoding modules imported during every interpreter startup into
the CPython binary, eliminating filesystem I/O that is prohibitively slow on
Nanvix ramfs/microvm.

Motivation

During CPython startup, 25 modules are imported. Prior to this change, 20 were
frozen/builtin but the encodings package and its codecs required filesystem reads
from ramfs. On Nanvix each file open/read/close involves VM exits, adding
measurable latency to startup.

Changes

• Tools/build/freeze_modules.py: Add encodings package + 4 codec modules to FROZEN list
• Python/frozen.c: Auto-regenerated with 5 new frozen module entries
• Makefile.pre.in: Auto-regenerated with freeze targets for encoding modules
• PCbuild/_freeze_module.vcxproj{,.filters}: Auto-regenerated for Windows builds

Design Decision

Only the 5 startup-critical codecs are frozen (not all ~100 encoding modules):
encodings, encodings.aliases, encodings.ascii, encodings.latin_1, and
encodings.utf_8. Binary growth is ~92 KB.

Benchmark

Platform: microvm/standalone, 128 MB, Nanvix v0.12.364
Method: 20 A/B interleaved pairs on WSL2 (i9-12900H, KVM)

Metric	Baseline	Frozen	Delta
Mean	79.8 ms	78.0 ms	-1.8 ms (2.3%)
Median	79.0 ms	70.5 ms	-8.5 ms (10.8%)
P10	64 ms	58 ms	-6 ms
P90	109 ms	119 ms	+10 ms
Binary size	15.8 MB	15.9 MB	+92 KB
Frozen wins	-	-	13/20 pairs

The improvement is modest on a fast KVM host (~80 ms total startup).
On production Nanvix deployments with higher VM-exit latency the saving
scales proportionally.

Supersedes the earlier revision of #317 which included pre-compiled .h
headers in the commit. This version relies on the build system to
generate them, matching upstream CPython conventions.

[Copilot]

Pull request overview

This PR aims to freeze the full encodings.* package into the CPython binary to reduce startup time by eliminating filesystem I/O during interpreter initialization (especially impactful in the Nanvix/ramfs environment).

Changes:

• Enable freezing of all encodings.* modules via Tools/build/freeze_modules.py.
• Extend the frozen module registry (Python/frozen.c) and build rules (Makefile.pre.in, PCbuild/_freeze_module.*) to include the encodings modules.
• Add a guard in Python/import.c to avoid crashing when a deepfrozen-only module has no marshalled byte buffer in subinterpreters.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Tools/build/freeze_modules.py	Enables freezing of encodings.* via the module selection list.
Python/import.c	Prevents NULL deref/crash when unmarshalling deepfrozen-only modules in subinterpreters.
Python/frozen.c	Adds encodings frozen entries + os.path platform mapping; updates frozen module tables.
Makefile.pre.in	Adds freeze/deepfreeze inputs/outputs and per-module freeze targets for encodings on POSIX builds.
PCbuild/_freeze_module.vcxproj	Adds Windows freeze targets for encodings modules.
PCbuild/_freeze_module.vcxproj.filters	Adds encodings sources into the Visual Studio filter list.

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[Copilot]

Pull request overview

This PR reduces CPython interpreter startup latency on Nanvix by freezing the small set of encoding-related modules that are imported on every startup into the binary, avoiding slow ramfs filesystem I/O during initialization.

Changes:

• Add encodings (package) and four startup-critical codec modules to the frozen stdlib startup set.
• Regenerate frozen-module artifacts (Python/frozen.c, Makefile.pre.in, and Windows freeze project files) to include the new modules.

Show a summary per file

File	Description
Tools/build/freeze_modules.py	Adds encodings + key codec modules to the “startup, without site” frozen module list.
Python/frozen.c	Registers the new frozen modules (includes, externs, and stdlib_modules[] entries).
Makefile.pre.in	Adds the new inputs/outputs and per-module freeze targets for POSIX builds and deepfreeze dependency lists.
PCbuild/_freeze_module.vcxproj	Adds the new modules to the Windows frozen-header generation and deepfreeze command list.
PCbuild/_freeze_module.vcxproj.filters	Adds the new Python source entries to the Visual Studio filters list.

Copilot's findings

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• Files reviewed: 5/5 changed files
• Comments generated: 0 new