fix: simplify artifact cache pruning

[peters]

Summary

• remove the extra install artifact cache prune-stat wrapper and use the shared prune helper directly
• keep CLI prune logging concise while making GUI/headless install pruning silent best-effort
• keep the release workflow on NuGet.org publishing and the supported checkout action version

Validation

• ./scripts/sync-surge-core-vendor.sh --check
• ./scripts/check-version-sync.sh
• cargo fmt --all -- --check
• RUSTFLAGS="-D warnings" cargo test --workspace
• cargo clippy --all-targets --all-features -- -D warnings
• cargo clippy --workspace --lib --bins --examples -- -D warnings -D clippy::unwrap_used -D clippy::expect_used
• cargo clippy --workspace --all-targets --all-features -- -D warnings -W clippy::pedantic
• dotnet format dotnet/Surge.slnx --verify-no-changes
• dotnet test dotnet/Surge.slnx --configuration Release

Notes

• The first local cargo test attempt needed network access to download the updated sysinfo crate from the refreshed base.
• The first local dotnet format attempt failed during restore under the sandbox, then passed with network-enabled restore.