Automate Pyodide cache staging and prep docs.rs builds

[moperacz]

Summary

• add full-pyodide-packages feature that lets the build script download and verify the full Pyodide 0.29.0 bundle, wiring the extracted cache into PyRuntimeConfig::default() when hosts opt in
• expose PyRuntimeConfig::set_pyodide_package_dir (and helpers) so embedders can configure the cache path programmatically, and update the package resolver to honour overrides before env vars
• extend the CLI with assets stage for staging full/core Pyodide bundles (checksums, force overwrite, archive reuse) and document the three supported cache provisioning paths
• ship .cargo/config.toml pointing RUSTY_V8_MIRROR at the PIC-enabled V8 142.0.0 release so downstream builds link cleanly without extra env plumbing; document the mirror and keep overrides available
• teach the build script to emit stub assets when DOCS_RS=1, add the docsrs feature/metadata, and enable doc_auto_cfg so crates.io/docs.rs builds succeed without network access
• refresh public docs to cover the new automation options, V8 mirror guidance, and cache override API

Testing

• cargo fmt -p aardvark-core
• cargo fmt -p aardvark-cli
• RUSTY_V8_MIRROR=/Users/misiek/Documents/projects/boa/tmp/v8-142.0.0 cargo test -p aardvark-core
• RUSTY_V8_MIRROR=/Users/misiek/Documents/projects/boa/tmp/v8-142.0.0 cargo test -p aardvark-cli
• RUSTY_V8_MIRROR=/Users/misiek/Documents/projects/boa/tmp/v8-142.0.0 cargo test --workspace

Follow-ups

• publish the PIC-enabled V8 142.0.0 archive referenced by the mirror and rerun CI without the local RUSTY_V8_MIRROR
• consider a CI-friendly smoke test for aardvark-cli assets stage (behind a feature flag to avoid network requirements)

[Copilot]

Pull Request Overview

This PR configures the V8 build to use position-independent code (PIC) by default, enabling downstream shared library integrations (such as Elixir NIFs) to link against V8 without encountering relocation errors.

Key Changes:

• Sets force_pic=true in V8's GN build arguments via cargo configuration
• Documents the new build configuration and its purpose

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.cargo/config.toml	Adds environment variable to force PIC in V8 builds
docs/dev/environment.md	Documents the PIC configuration and new EXTRA_GN_ARGS environment variable

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[Copilot]

Pull Request Overview

Copilot reviewed 26 out of 27 changed files in this pull request and generated 1 comment.

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