Static schemas (tasks, snippets, jsonc, keymap, action/*, tsconfig,
package_json, inspector_style) are now computed once on first access
using LazyLock and returned immediately via Task::ready().

These schemas never change at runtime because:
- tasks, snippets, jsonc, inspector_style are derived from static Rust
types
- tsconfig, package_json are bundled JSON files (include_str!)
- keymap and action/* depend only on registered actions, which are
collected at compile/link time via the inventory crate (extensions
cannot add actions)

This eliminates foreground thread blocking for these schema requests.

**New functions added to KeymapFile:**
- `generate_json_schema_from_inventory()`: generates keymap schema
without App context
- `get_action_schema_by_name()`: looks up single action schema without
App context

Release Notes:

- N/A

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>