fix(codegen): non-deterministic ordering in Python msgspec generator

[YuanYuYuan]

Summary

hiroz-codegen's Python msgspec generator uses HashMap<String, Vec<&ResolvedMessage>> to group messages by package. HashMap iteration order is non-deterministic, so rebuilding produces a different class ordering in the generated crates/hiroz-msgs/python/hiroz_msgs_py/types/*.py files each time. This causes spurious diffs after any cargo build or cargo check run.

Root Cause

crates/hiroz-codegen/src/python_msgspec_generator.rs:

• packages: HashMap<String, Vec<&ResolvedMessage>> — package iteration order is random
• service_messages: HashMap<String, Vec<&ResolvedMessage>> — same
• service_hashes: HashMap<String, HashMap<String, String>> — same
• The message vec within each package also reflects HashMap insertion order

Fix

Replace all HashMap<String, Vec<...>> keyed on String with BTreeMap<String, Vec<...>> in the generator. BTreeMap iterates in sorted key order, making the output fully deterministic. Also sort each message vec by name before generating (sort_by_key(|m| &m.parsed.name)).

Impact

• Dirty worktrees after any build that triggers codegen
• Noisy git diff that looks like real changes
• Risk of accidentally committing a reshuffled file as if it were meaningful