fix: configure cross-compilation environment for OpenSSL and RocksDB

[JoshuaBatty]

This job failed when building forc-node. I've updated the below to use the same process as the sway repo and bumped forc-node to 0.71.1 to cut a new release once this lands.

• Add setup-cross-build action to configure Docker images with OpenSSL dev headers for ARM64 Linux cross-compilation
• Add cross_image to Linux matrix entries for custom Docker builds
• Add Prepare RocksDB build env step for bindgen/libclang on Linux
• Add permissions: contents: write for release asset uploads
• Update checkout to v4 and rust-cache to v2
• Use pinned RUST_VERSION instead of stable

[cursor]

PR Summary

Improves release build reliability by setting up proper Linux cross-compilation tooling and updating forc-node versioning.

• Add setup-cross-build action and cross_image entries for Linux targets; build with cross
• New RocksDB/Bindgen setup on Linux (install clang/llvm, set LIBCLANG_PATH and BINDGEN_EXTRA_CLANG_ARGS)
• Update actions (checkout@v4, rust-cache@v2) and grant permissions: contents: write for release uploads
• Bump forc-node to 0.71.1 with changelog; update Cargo.lock

^{Written by Cursor Bugbot for commit d0ee834. This will update automatically on new commits. Configure here.}

[github-actions]

LCOV of commit d0ee834 during CI #42

Summary coverage rate:
  lines......: 44.3% (1249 of 2822 lines)
  functions..: 34.0% (155 of 456 functions)
  branches...: 28.9% (63 of 218 branches)

Files changed coverage rate: n/a