[Storage] Widen AccessPolicy.start/expiry alternateType scope to include python (#42857)

BlobStorage and QueueStorage AccessPolicy.start/expiry are encoded as rfc3339-fixed-width (sub-second precision). Python's emitter loses precision when these are kept as utcDateTime, just as JavaScript does. Widen the existing 'javascript' alternateType scope to 'javascript, python' so the Python SDK receives them as strings, matching the treatment already used in FileStorage.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: l0lawrence

specification/storage/Microsoft.BlobStorage/client.tsp

@@ -143,8 +143,8 @@ interface PageBlobClient extends Storage.Blob.PageBlob {}
   "python, csharp, javascript"
 );
 
-@@alternateType(AccessPolicy.start, string, "javascript");
-@@alternateType(AccessPolicy.expiry, string, "javascript");
+@@alternateType(AccessPolicy.start, string, "javascript, python");
+@@alternateType(AccessPolicy.expiry, string, "javascript, python");
 @@alternateType(UserDelegationKey.signedStart, string, "javascript");
 @@alternateType(UserDelegationKey.signedExpiry, string, "javascript");
 @@alternateType(MultipartBodyParameter.body, string, "javascript");

specification/storage/Microsoft.QueueStorage/client.tsp

@@ -170,8 +170,8 @@ model SignedIdentifiersGo is Array<SignedIdentifier>;
   "nextVisibleOn",
   "javascript"
 );
-@@alternateType(AccessPolicy.start, string, "javascript");
-@@alternateType(AccessPolicy.expiry, string, "javascript");
+@@alternateType(AccessPolicy.start, string, "javascript, python");
+@@alternateType(AccessPolicy.expiry, string, "javascript, python");
 @@clientName(AccessPolicy.start, "startsOn", "javascript");
 @@clientName(AccessPolicy.expiry, "expiresOn", "javascript");
 @@clientName(AccessPolicy.permission, "permissions", "javascript");