[performance][medium] Cache parsed configuration to avoid repeated JSON reloading

[upupwrite]

Summary

The application repeatedly reads and parses the JSON configuration (File::loadConfig and related helpers) on many code paths (e.g., getCommandIndex, interactiveSearch). Re-parsing and reloading the config for frequent operations adds CPU and I/O overhead, especially for large configurations or when performing many interactive searches in a session.

Reproduction / evidence

• src/loadfile.cpp: File::getCommandIndex calls loadConfig() at the start of the function. Similar patterns appear in other call sites that run during interactive flows.

Impact

• Increased latency when listing/searching commands or when the CLI performs frequent operations.
• Unnecessary disk I/O and CPU usage for repeated JSON parsing.

Suggested fixes / improvements

1. Implement an in-memory config cache:

   • Load and parse the configuration once at startup or on first access and keep it in memory.
   • Invalidate and reload the cache only when the config file changes (watch file mtime or provide an explicit reload API).

2. Use incremental updates for small modifications:

   • When the program modifies a single command or alias, update the in-memory structure and persist the change rather than reloading the entire file.

3. Reduce JSON parsing overhead:

   • Consider using a faster JSON library or enable streaming parsing for large files. Profile current parsing to determine hotspots.

Files/places to review first

• src/loadfile.cpp (loadConfig, saveConfig, getCommandIndex)
• Any code that calls loadConfig frequently during interactive flows

Severity: medium