ci: make release publishing idempotent

[AlainDor]

Summary

• make real release publishes create or reuse the GitHub Release from the workflow
• upload release assets with clobber when the release already exists
• skip crates.io publish and dry-run steps when the target crate version already exists

Verification

• cargo build --workspace
• cargo test --workspace
• cargo test --workspace --all-features
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo deny check
• cargo package --workspace --allow-dirty
• yq eval '.' .github/workflows/release.yml >/dev/null
• git diff --check