feat(ksuid): add BinExpr, flexible parsers, and expression helpers

Adds ParseStringKSUIDAny, ParseBinaryKSUIDAny, BinaryKSUID.BinExpr, and
ExprStringKSUIDs for portal-compatible KSUID handling at API boundaries.

Co-authored-by: Cursor <cursoragent@cursor.com>

doc.go

@@ -28,7 +28,8 @@
 // SQL encoding. Both implement [ApplyInterface] via Equal and IsZero for use
 // with [ApplyInterfacePtr]. Both share identical GraphQL string scalar transit.
 // Choose StringKSUID for text columns (VARCHAR, TEXT); choose BinaryKSUID for
-// binary columns (BINARY(20), BYTEA).
+// binary columns (BINARY(20), BYTEA). [ParseStringKSUIDAny] and
+// [ParseBinaryKSUIDAny] accept flexible input for API boundaries.
 //
 // [JSONB] provides map-based JSON column scanning for Postgres JSONB and MySQL JSON.
 //