ci: isolate release job toolchain state

[cbusillo]

Summary

• isolate release preflight and build jobs with per-job CARGO_HOME and RUSTUP_HOME under runner.temp
• stop deleting Cargo git/registry state before rust-cache post-job teardown
• make Linux package installs use sudo only when available, root when already root, and clear errors when required tools are missing

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release.yml"); puts "yaml ok"'
• git diff --check
• rg sweep for removed sudo/setup-python/shared-cargo patterns
• ./build-fast.sh

Refs #87