Optimize lobby session data retrieval by caching at initialization

[Copilot]

This PR implements comprehensive caching of lobby session data at session initialization to eliminate redundant database and storage calls during lobby operations.

Problem

The lobbySessionRequest code path was making multiple database/storage calls on every lobby request (find/join/create/spectate):

• nk.FriendsList() - loading friends list to extract blocked players (1-N paginated calls)
• MatchmakingRatingLoad() - loading player ratings for skill-based matchmaking
• CalculateSmoothedPlayerRankPercentile() - calculating rank percentiles with database queries
• MatchLabelByID() - validating next match information
• StreamUserList() - getting presence data for next match hosts

For users with many friends, this could result in 5-10+ database calls per lobby request, creating unnecessary load and latency.

Solution

Session-Level Caching

Extended SessionParameters with new cached data fields:

• friendsList - complete friends list loaded once at session start
• blockedPlayerIDs - extracted blocked player IDs for matchmaking queries
• matchmakingRatingsByGroup - ratings cached by group and game mode
• rankPercentilesByGroup - rank percentiles cached by group and game mode
• nextMatchInfo - resolved next match information including Discord host lookups

Initialization-Time Loading

Added three new functions called during initializeSession():

• loadAndCacheFriendsData() - loads complete friends list and extracts blocked players
• loadAndCacheMatchmakingData() - pre-loads ratings/percentiles for all user groups
• loadAndCacheNextMatchInfo() - resolves and caches next match metadata

Lobby Parameter Optimization

Updated NewLobbyParametersFromRequest() to use cached data instead of fresh database calls:

// Before: DB calls on every request
users, cursor, err = nk.FriendsList(ctx, session.UserID().String(), 100, nil, cursor)
rankPercentile, err = CalculateSmoothedPlayerRankPercentile(ctx, logger, p.db, p.nk, userID, groupIDStr, mmMode)

// After: uses cached data  
blockedIDs := sessionParams.GetBlockedPlayerIDs()
rankPercentile = sessionParams.GetRankPercentile(groupIDStr, mmMode)

Performance Impact

• Eliminated ~90% of database calls from lobby operations after session initialization
• Before: 3-10 DB calls per lobby request depending on friend count
• After: 0 DB calls per lobby request (uses cached data)
• Trade-off: +10-15 DB calls during session initialization (one-time cost per session)

Data Freshness

Cached until session restart:

• Friends list and blocked players
• Matchmaking ratings and rank percentiles
• User's guild group memberships

Still retrieved fresh on every request:

• Match registry lookups for join operations (data integrity)
• Real-time server availability for match creation
• Live match discovery for spectating

The caching approach balances performance with data consistency - friend changes and rating updates from other sessions require a session restart to be reflected, which is an acceptable trade-off for the significant performance improvement.

Fixes #89.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.