refactor: remove unused mockall, fix flaky tests

- Remove mockall = "0.14.0" from desktop/src-tauri dev-dependencies
  (never used, project policy forbids mocks in tests)
- Fix test_save_one_memory in terraphim_config: handle global storage
  singleton already initialized by other tests with different profiles
- Fix test_circuit_breaker_half_open_after_cooldown in terraphim_spawner:
  increase sleep margin from 5ms to 50ms to prevent flaking under load

Most dependency duplicates (ahash 0.7/0.8, toml 0.5/0.9, lru 0.7/0.16,
thiserror 1.0/2.0) are transitive and unavoidable without upstream
crate changes.

Refs: #627

Co-Authored-By: Terraphim AI <noreply@anthropic.com>

Author: 2 people

desktop/src-tauri/Cargo.toml

@@ -67,7 +67,7 @@ lru = "0.16"
 tokio-test = "0.4.4"
 serial_test = "3.3.1"
 tempfile = "3.23.0"
-mockall = "0.14.0"
+
 
 [features]
 # by default Tauri runs in production mode