[P1] Test infrastructure: Hilt test modules and :core:testing fakes

[amaury901130]

Remove mutable ServiceProviderModule.URL_API static; use @TestInstallIn modules. Replace removed TestCoroutineDispatcher with StandardTestDispatcher/MainDispatcherRule. Shared fakes in :core:testing.

Acceptance criteria

• No test hooks in production code
• Tests use kotlinx-coroutines-test current APIs

Reference: Android Base — Modernization Audit & Recommendations — section: Findings > Security / Tooling