PERF-17/PERF-18 · Simplify ProcessorFactory and repository construction (remove reflection/double lookups)

[LarsLaskowski]

Finding: PERF-17 (Low) + PERF-18 (Low) · Area: F1Server.Service / F1Server.Db
Source: docs/concepts/udp-packet-processing-performance-review.md (branch claude/udp-packet-processing-review-798u7o), section 2.3

Files involved

• F1Server.Service/Processors/ProcessorFactory.cs:113-375 — nine near-identical Get{X}Processor methods, each doing ContainsKey + TryGetValue (double hash lookup per packet) and creating via Activator.CreateInstance
• F1Server.Db/Entity/RepositoryFactory.cs:92-102 — GetRepository<T> constructs repositories via Activator.CreateInstance
• F1Server.Db/Entity/Repositories/Base/RepositoryBase{TQueryable,TEntity}.cs:65-68 — GetQuery() uses Activator.CreateInstance per query

Problem / Impact

Small but constant reflection and double-lookup overhead multiplied by per-packet/per-query call frequency, plus ~250 lines of copy-paste in ProcessorFactory.

Step-by-step fix

1. ProcessorFactory: replace the nine Get{X}Processor methods with one private generic helper:

   private TProcessor GetOrCreateProcessor<TProcessor>(Func<TProcessor> factory)
       where TProcessor : BaseProcessor
   {
       return (TProcessor)_processors.GetOrAdd(typeof(TProcessor), _ => factory());
   }

   and call it from the switch in GetProcessor with direct constructors, e.g. PacketTypes.Session => GetOrCreateProcessor(() => new SessionProcessor(_serviceProvider, packetHeader, gameInfo)). Behavior note: RemoveAllProcessors() on session change and the frame-identifier logic in GetProcessor stay exactly as they are.
2. RepositoryFactory.GetRepository: cache compiled constructor delegates in a private static readonly ConcurrentDictionary<Type, Func<F1ServerDbContext, RepositoryBase>>, built once per repository type via Expression.New + Expression.Lambda. The per-instance _repositories dictionary stays (same semantics), only the creation path changes.
3. GetQuery(): same approach — a static compiled delegate per TQueryable type (Func<IQueryable<TEntity>, TQueryable>), replacing Activator.CreateInstance(typeof(TQueryable), ...).
4. Note: all affected classes are internal/public with known constructor signatures — if a constructor signature does not match at delegate-build time, fail fast with a clear exception message.

Test guidance

Existing processor and repository tests cover the behavior; they must stay green unchanged. Add one test asserting ProcessorFactory.GetProcessor returns the same instance for two packets of the same type and session, and a new instance after a session-id change (this pins the caching semantics the refactor must preserve).

Acceptance criteria

• No Activator.CreateInstance in the per-packet or per-query path
• ProcessorFactory caching implemented once (generic helper), nine copies removed
• Processor-caching semantics pinned by a test (same session → same instance; new session → fresh instances)
• Full rebuild shows 0 Reihitsu (RH####) warnings

Related: #420 (long-lived factories reduce how often the repository delegates run — still worth removing the reflection).