[VMOwnedVolumes][Draft]Introduce new CNS apis

[deepakkinni]

Description

Adds govmomi Go bindings for three new CNS VolumeManager APIs that implement a two-phase FCD unregister protocol, required for the VM-owned volumes feature (VMOwnedVolumes):

• CnsUnregisterVolumeEx (async, returns vim.Task): Phase 1 of the two-phase unregister. Removes the FCD catalog/DDB entries and persists a PENDING_UNREGISTER record in the CNS database containing the backingDiskPath and diskUUID. The task result is a CnsUnregisterVolumeResult (new type extending CnsVolumeOperationResult) with those fields populated.
• CnsAcknowledgeUnregister (synchronous, void): Phase 2. Deletes the PENDING_UNREGISTER record from the CNS database. Idempotent — safe to call multiple times.
• CnsQueryPendingUnregisters (synchronous): Crash-recovery query. Returns all outstanding PENDING_UNREGISTER records so the caller can resume any in-flight two-phase operations after a restart.

Changes:

• cns/types/types.go: New CnsUnregisterVolumeResult struct (embeds CnsVolumeOperationResult, adds BackingDiskPath and DiskUUID); request/response types for all three APIs.
• cns/methods/methods.go: SOAP Body structs and RoundTrip wrapper functions for all three APIs.
• cns/client.go: High-level client methods UnregisterVolumeEx, AcknowledgeUnregister, and QueryPendingUnregisters.
• cns/simulator/simulator.go: In-memory simulator handlers for all three APIs, including a pendingUnregisters map on CnsVolumeManager that tracks phase-1 records until acknowledged.
• cns/simulator/simulator_test.go: TestUnregisterVolumeEx exercising the full two-phase lifecycle: create volume → unregister (phase 1, verify BackingDiskPath/DiskUUID in result) → query pending (verify record present) → acknowledge (phase 2) → query pending (verify empty) → idempotent re-acknowledge (verify no error).
  Are there any special notes for your reviewer:
  The CnsUnregisterVolumeResult type is registered in the type system without the vsan: prefix (consistent with other result types like CnsVolumeCreateResult, CnsVolumeAttachResult) so that SOAP XML deserialization of the polymorphic volumeResults array works correctly.

Closes: #(issue-number)

How Has This Been Tested?

Please describe any manual tests done to verify your changes.

Guidelines

Please read and follow the CONTRIBUTION guidelines of this project.

[tenthirtyam]

Needs a gofmt.