Asset Modules: Introduce session manager with one id per download request

[EDWARD-012]

Summary

Implements a Play-like asset module session manager for #2675 (follow-up to #2506).

Each startDownload allocates one ever-increasing global session id that covers all requested modules. Replaces per-module base + moduleIndex assignment. requestDownloadInfo does not allocate sessions.

Changes

• Add AssetModuleSessionManager (SharedPreferences AssetModuleSessionIdGenerator / Latest)
• Bind all modules in a request to one sessionId (keep sessionIds map with identical values)
• Fix onStartDownload to pass the real session id; pack-scoped session_id is never status
• getSessionStates returns one bundle per session
• On rebind, rename existing module dirs into the new session path when present

Out of scope

• Download cancellation (Asset Modules download cancellation incomplete #2673)
• Early temp cleanup (Remove temporary asset module files as early as possible #2674)
• Device Sync

Test plan

• :vending-app:assembleDefaultDebug / lintDefaultDebug
• Single-module game still downloads (e.g. mkx / gameloft / pesam)
• Multi-module fetch shares one session_id
• Repeat startDownload gets a new session id
• requestDownloadInfo does not mint a new session

Fixes #2675