Add hash collision test for NodeType ID generation

[tmchow]

Adds tests for nodeTypeIdFromTaintsAndLabels that verify:

1. No hash collisions across realistic Kubernetes taint/label combinations (taint keys x effects, label keys x values, mixed taint+label inputs)
2. The hash is never zero, even for empty inputs

Tests 60+ unique inputs with zero collisions observed. Removes the TODO comment that requested this coverage.

Closes #4778

This PR was authored by a human with AI coding assistance.

[greptile-apps]

Greptile Summary

This PR adds hash collision tests for nodeTypeIdFromTaintsAndLabels (closing #4778) and bundles a bonus refactoring that replaces all plain-string context keys ("principal", "user", "requestId") with a new typed ctxkeys.ContextKey type, preventing accidental collisions between packages. All writers and readers of those context values have been updated consistently, and a grep across the repository confirms no stale plain-string lookups remain.

Confidence Score: 5/5

This PR is safe to merge; all changes are either test additions or a consistent typed-key refactor with no remaining plain-string callers.

The collision tests are correct and cover the stated combinations. The ctxkeys refactoring is complete — every writer and reader was updated together, the grep finds no leftover plain-string lookups, and the test files were updated in lockstep. No logic was changed in production code outside of the key type.

No files require special attention.

Important Files Changed

Filename	Overview
internal/scheduler/internaltypes/node_type_test.go	Adds two new tests: collision detection across 60+ realistic taint/label combinations and a zero-hash guard; logic is correct and the TODO is removed.
internal/common/ctxkeys/ctxkeys.go	New package that introduces a typed ContextKey string type and three constants (PrincipalKey, UserKey, RequestIDKey) to replace plain string context keys across the codebase.
internal/common/auth/common.go	Migrates principalKey from a plain string literal to ctxkeys.PrincipalKey typed constant; all readers (GetPrincipal) and writers (WithPrincipal) are updated consistently.
internal/common/armadacontext/armada_context.go	FromGrpcCtx now reads "user" and "requestId" via typed ctxkeys constants instead of plain strings, consistent with the writers in auth and requestid packages.
internal/common/requestid/interceptors.go	AddToIncomingContext now stores the request ID using ctxkeys.RequestIDKey instead of the plain string "requestId".
internal/common/grpc/grpc.go	InterceptorLogger reads user and requestId from context via typed ctxkeys constants, completing the migration away from plain string keys.
internal/server/submit/submit_test.go	Test setup updated to store the principal using ctxkeys.PrincipalKey so it is found by GetPrincipal after the typed-key migration.
internal/scheduler/internaltypes/node_type.go	Removed the TODO comment requesting hash-collision test coverage; no logic changes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Incoming gRPC request] --> B[requestid.UnaryServerInterceptor]
    B --> C["context.WithValue(ctx, ctxkeys.RequestIDKey, id)"]
    C --> D[auth.CreateGrpcMiddlewareAuthFunction]
    D --> E["context.WithValue(ctx, ctxkeys.UserKey, name)"]
    E --> F["WithPrincipal → context.WithValue(ctx, ctxkeys.PrincipalKey, principal)"]
    F --> G[Handler / interceptors read context]
    G --> H["grpc.InterceptorLogger\nctx.Value(ctxkeys.UserKey)\nctx.Value(ctxkeys.RequestIDKey)"]
    G --> I["auth.GetPrincipal\nctx.Value(ctxkeys.PrincipalKey)"]
    G --> J["armadacontext.FromGrpcCtx\nctx.Value(ctxkeys.UserKey)\nctx.Value(ctxkeys.RequestIDKey)"]

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_{Reviews (3): Last reviewed commit: "Fix submit_test.go to use typed context ..." | Re-trigger Greptile}