fix(ci): resolve Launchpad PPA build failures with Rust 1.85 compatibility

[appleparan]

Summary

• Fix Launchpad PPA build failures by ensuring Rust 1.85 compatibility
• Add CI workflow to test Launchpad build environment before uploading
• Pin dependencies to versions compatible with Rust 1.85 (Launchpad's toolchain)

Problem

Launchpad PPA builds were failing due to:

1. Dependency incompatibility: Several crates require Rust versions newer than 1.85
   • sysinfo@0.37.2 requires Rust 1.88
   • libloading@0.9 requires Rust 1.88
   • libamdgpu_top@0.11 uses Rust 2024 edition (requires Rust 1.88+)
2. Unstable feature usage: Code used is_multiple_of() which is unstable until Rust 1.88+ (rust-lang/rust#128101)
3. No pre-upload testing: No way to verify builds would succeed on Launchpad before uploading

Solution

1. Pin dependencies to Rust 1.85-compatible versions:
   • sysinfo: 0.37 → 0.33 (MSRV 1.69)
   • libloading: 0.9 → 0.8 (MSRV 1.71)
   • libamdgpu_top: 0.11 → 0.10 (uses Rust 2021 edition)
2. Replace unstable feature: Use cycle % FULL_REFRESH_INTERVAL == 0 instead of cycle.is_multiple_of()
3. Add clippy lint allowances for cross-version compatibility:
   • manual_is_multiple_of = "allow" in Cargo.toml (for latest Rust)
   • #[allow(clippy::needless_lifetimes)] on 9 impl blocks (for Rust 1.85)
4. Add Launchpad build test CI (launchpad_build_test.yml):
   • Tests offline build with --network none (simulates Launchpad)
   • Tests with Rust 1.85 toolchain
   • Runs on push/PR to catch issues early

Test Plan

* `cargo build --release` passes with latest Rust
* `cargo build --release` passes with Rust 1.85
* `cargo clippy --release -- -D` warnings passes with latest Rust
* `cargo clippy --release -- -D` warnings passes with Rust 1.85
* `cargo test` passes
* Launchpad PPA build succeeds after merge

Closes #112