feat: add python 3.7 and wasm runtimes

[loonghao]

Summary

• add legacy Python 3.7.9 support via python-build-standalone 20200822 assets and layout
• add Wasmtime and Wasmer providers, with Wasmer using archive assets instead of the Windows installer
• update provider documentation/counts to 142

Validation

• vx just quick
• vx just docs-build
• focused provider tests for Python 3.7, Wasmer, Wasmtime, and provider lint
• local smoke: python@3.7, wasmtime, and wasmer@7.1.0