feat(offchain): new JD in memory client (#518)

Added a pure in memory JD client for testing purposes.

Author: graham-chainlink

.changeset/gold-frogs-enjoy.md

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+---
+"chainlink-deployments-framework": minor
+---
+
+feat(offchain): new JD in memory client

offchain/jd/memory/doc.go

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+// Package memory provides an in-memory implementation of the Job Distributor client.
+//
+// This package is designed for testing purposes when you don't need a real JD backend.
+// All data is stored in memory and is lost when the client is garbage collected.
+//
+// # Thread Safety
+//
+// The MemoryJobDistributor implementation is thread-safe and uses sync.RWMutex to protect
+// concurrent access to internal data structures. Multiple goroutines can safely call methods
+// on the same MemoryJobDistributor instance concurrently.
+//
+// # Usage
+//
+// Create a new in-memory JD client:
+//
+//	client := memory.NewMemoryJobDistributor()
+//
+// Use it like any other JD client:
+//
+//	resp, err := client.ProposeJob(ctx, &jobv1.ProposeJobRequest{
+//	    NodeId: "test-node",
+//	    Spec:   "job spec here",
+//	})
+//
+// # Limitations
+//
+// - No persistence: All data is stored in memory only
+// - Test-only: This implementation is intended for testing and should not be used in production environments
+//
+// # Implementation Details
+//
+// The client maintains four in-memory maps:
+//   - jobs: Stores job instances by job ID
+//   - proposals: Stores job proposals by proposal ID
+//   - nodes: Stores node registrations by node ID
+//   - keypairs: Stores CSA keypairs by public key
+//
+// All write operations (create, update, delete) modify these maps directly,
+// and read operations return data from these maps.
+package memory