feat: add statically compiled native-tls to binary

[b4iterdev]

Summary

Originally native-tls pulls in openssl as a transitive dependency for IMAP support, and native-tls doesn't use the vendored feature by default. It links against the system's libssl, which on Debian Trixie is OpenSSL 3.x (libssl3), not libssl.so.1.0.0. As a result, running openfang on Debian trixie will results in

openfang: error while loading shared libraries: libssl.so.1.0.0: cannot open shared object file: No such file or directory

This PR add features = ["vendored"] into native-tls. Which causes it (and the imap crate's transitive OpenSSL dependency) to statically compile OpenSSL rather than link against the system's libssl at runtime. The binary will no longer depend on libssl.so.1.0.0 being present on the target system.

Previously, commit 135c37f adds features = ["vendored"] to openssl, however it does not fully resolve the linking issue.

Changes

• Cargo.toml: add features = ["vendored"] to native-tls

Testing

• cargo clippy --workspace --all-targets -- -D warnings passes: Proof
• cargo test --workspace passes: Proof
• Live integration tested (if applicable): Installed binary with existing Github Action workflow on Debian trixie and the problem no longer exists

Security

• No new unsafe code
• No secrets or API keys in diff: N/A
• User input validated at boundaries: N/A