Apply review-thread exception message updates for Get-NFSDatastoreNConnectValue

[Copilot]

The follow-up addresses all comments in review thread pullrequestreview-4128413142 with only the requested scope. Suggested changes were applied as-is, and tests were aligned to the resulting exception contract.

The changes in this PR are as follows:

• Function exception contract alignment
  • Updated Get-NFSDatastoreNConnectValue datastore-not-found error text to match the exact review suggestion (removed cluster-filter phrasing).
• Focused test expectation updates
  • Updated Microsoft.AVS.NFS.Tests.ps1 expected exception messages to match the reviewed/implemented throw messages for:
    • datastore not found
    • host-level nConnect retrieval failure
    • cluster lookup failure
    • datastore lookup failure
• Example (applied suggestion shape)

  throw [System.Management.Automation.PSArgumentException]::new("Datastore '$DatastoreName' was not found in vCenter inventory.")

I have read the contributor guidelines and have completed the following:

• Formatted the code using VSCode default formatter for PowerShell.
• Tested the code end-to-end against an SDDC.
• Documented the functions using standard PowerShell markup and applied AVSAttribute to newly exported functions.