Fix recursive_update_dict to add new keys from project config

[nulinspiratie]

Summary

Fixes a bug in recursive_update_dict() that prevented project-specific configuration from adding new keys that didn't exist in the base config.

Problem

The recursive_update_dict() function in qualibrate_config/core/utils.py was skipping keys that didn't exist in the base dictionary:

for k, v in updates.items():
    if k not in to_update:
        continue  # ← BUG: Skips new keys instead of adding them!

This caused project configuration overrides to be silently ignored when they tried to add new configuration keys.

Real-World Impact: QUAM State Path

This bug particularly affected QUAM's state_path configuration:

Base config (~/.qualibrate/config.toml):

[quam]
raise_error_missing_reference = false
version = 3

[qualibrate]
project = "CS_1"

Project config (~/.qualibrate/projects/CS_1/config.toml):

[quam]
state_path = "/path/to/project/quam_state"

Expected behavior: Project's state_path should be merged into the final config
Actual behavior: state_path was silently skipped, causing QUAM to not recognize project-specific state paths

User Experience

When users switched projects and tried to load QUAM state:

from quam.config import get_quam_config
cfg = get_quam_config()
cfg.state_path  # ← Returns None instead of project-specific path!

This made project-based workflows impossible, as QUAM couldn't locate project-specific state files.

The Fix

Changed line 12 to add new keys instead of skipping them:

for k, v in updates.items():
    if k not in to_update:
        to_update[k] = v  # ← Now adds new keys
        continue
    # ... rest of merge logic

Testing

Verified the fix with:

1. Unit tests: New keys are properly added during merge
2. Integration test: Real config with CS_1 project now correctly returns project-specific state_path

Before fix:

cfg.state_path  # None

After fix:

cfg.state_path  # PosixPath('/path/to/project/quam_state')

Impact

• ✅ Project-specific config overrides now work for all configuration keys
• ✅ No changes to existing merge behavior for updating existing keys
• ✅ No breaking changes to API

Related Issues

This completes the fix for project-aware QUAM configuration, which also required removing the @cache decorator from get_quam_config() in the QUAM repository.

[natangqm]

can you explain what this function is doing?

[nulinspiratie]

Added docstring, does this clarify it?