chore(changeset): bump to minor — public bulk types widened

Per Lindsay's review on #493: the public type signatures shifted
(BulkEncryptPayload, BulkEncryptedData, BulkDecryptPayload,
BulkDecryptedData, and EncryptedQueryResult all admit null in element
positions, where they used to be narrow). Patch undersells that for SDK
consumers — bumping to minor.

Author: coderdan

.changeset/restore-null-guards-in-encryption-ops.md

@@ -1,5 +1,5 @@
 ---
-"@cipherstash/stack": patch
+"@cipherstash/stack": minor
 ---
 
 Fix: restore runtime null short-circuits in the encryption operation classes.