Add fast-path message destination cache

[ReubenBond]

Summary

• Adds a fast-path message destination cache for client/runtime message routing, caching resolved receivers on grain references/messages and reusing valid activation, connection, gateway, and hosted-client receivers.
• Invalidates stale cached receivers and falls back to normal addressing when connections, activations, or client gateway state are no longer valid.
• Avoids caching system target destinations so gateway/liveness changes are re-evaluated; keeps direct gateway connections normalized and updates client grain-to-silo mappings from responses.

Validation

• git diff --check
• conflict-marker scan
• dotnet build src\Orleans.Core\Orleans.Core.csproj -m
• dotnet build src\Orleans.Runtime\Orleans.Runtime.csproj -m

Dependencies / notes

• This PR targets main, but is logically related to the message-oriented networking work and may need review/merge coordination with that PR.
• Additional coverage should exercise cache hit/miss, invalidation on disconnect/reconnect, stale receiver invalidation, gateway/loopback routing, system target routing, and retry behavior.

Microsoft Reviewers: Open in CodeFlow

[ReubenBond]

AdaptivePing perf comparison

Compared PR #10064 against upstream/main using the same AdaptivePing harness on both sides.

• Before: 1fde9816a3
• After: a9e77d7bf8
• Build: Release, net10.0
• Run: AdaptivePing_All with maxStableRounds: 3; warmup and measurement intervals remained at 5s each.
• Machine: Windows 10.0.26200, Intel Core i9-13900K, 24 cores / 32 logical processors, .NET SDK 10.0.203

Scenario	Before best	After best	Delta	Best concurrency (before -> after)
Hosted Client	13,139,689/s	14,946,934/s	+13.8%	100 -> 210
Client to Silo	665,756/s	871,160/s	+30.9%	160 -> 190
Client to 2 Silos	1,716,756/s	1,820,492/s	+6.0%	500 -> 570
Silo to Silo	727,909/s	1,235,012/s	+69.7%	150 -> 390