build!: update dependencies to latest

[jrandolf]

Summary

• update buffa, buffa-build, and buffa-codegen to 0.6
• update connectrpc to 0.6
• remove the old buffa git patch pin so published crates resolve directly
• refresh Cargo.lock with transitive dependency updates

Impact

This is marked breaking because the public dependency floor for buffa and connectrpc moves to their latest major/minor lines.

Validation

• cargo test --workspace
• cargo check --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings