Add armv7-unknown-linux-gnueabihf target

[Myshkouski]

Summary

This PR adds cross-compilation support for the armv7-unknown-linux-gnueabihf target to enable running OpenFang on 32-bit ARM devices (such as Raspberry Pi 2/3/4 running 32-bit ARM Linux distributions).

Changes

The armv7 target support has been implemented across the following files:

1. Cross.toml - Added cross-compilation configuration for armv7:

[target.armv7-unknown-linux-gnueabihf]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH",
  "apt-get update && apt-get install --assume-yes libssl-dev:$CROSS_DEB_ARCH"
]

2. .github/workflows/release.yml - Added armv7 to the CLI build matrix:

- target: armv7-unknown-linux-gnueabihf
  os: ubuntu-22.04
  archive: tar.gz

3. Build process - Uses cross for cross-compilation (lines 176-183 in release.yml):

- name: Install cross (Linux aarch64/armv7)
  if: matrix.target == 'aarch64-unknown-linux-gnu' || matrix.target == 'armv7-unknown-linux-gnueabihf'
  run: cargo install cross --locked

• name: Build CLI (cross)
  if: matrix.target == 'aarch64-unknown-linux-gnu' || matrix.target == 'armv7-unknown-linux-gnueabihf'
  run: cross build --release --target ${{ matrix.target }} --bin openfang

Testing

• cargo clippy --workspace --all-targets -- -D warnings passes
• cargo test --workspace passes
• Live integration tested (if applicable)

Security

• [*] No new unsafe code
• [*] No secrets or API keys in diff

[Jengro777]

Quick feedback from the community:
https://github.com/librefang/librefang