Similar pattern to HashBytea but uses base64 encoding (standard for XDR)
and supports variable-length data.

Changed OperationXDR field from string to XDRBytea for automatic
base64/BYTEA conversion.

Cast the base64 XDR string to XDRBytea for proper database storage.

- Change UNNEST cast from text[] to bytea[]
- Convert XDRBytea to raw bytes in BatchInsert
- Update BatchCopy to pass raw bytes instead of pgtype.Text

Forces GraphQL to use a resolver for operationXdr to convert
XDRBytea to base64 string for API consumers.

- Update test_utils.go to use types.XDRBytea
- Regenerate GraphQL code with OperationXdr resolver

Returns the XDRBytea as a base64-encoded string for API consumers.

- Use parameterized queries with XDRBytea for SQL inserts
- Update assertions to use .String() for comparison
- Fix type casting in test data creation

- Use base64-encoded test XDR data in test_utils.go
- Add testOpXDR helper functions in test files
- Update all assertions to use .String() method

- Update createTestOperation to use proper base64 XDR
- Update generateTestOperations to encode test data as base64
- Update operations_test.go with base64 encoding for all test XDR data
- Fix assertions to compare against the stored XDRBytea values

This simplifies the XDR storage flow by storing raw bytes directly
instead of encoding to base64 and then decoding. The String() method
now handles base64 encoding for external representation.

Skip the intermediate base64 encoding step by using MarshalBinary()
instead of MarshalBase64(). The raw bytes are now stored directly
in XDRBytea.

Remove unnecessary Value() calls since XDRBytea is now []byte.
Access raw bytes directly via type conversion.

Decode expected base64 XDR string to raw bytes for comparison
since XDRBytea now uses []byte underlying type.

Use raw bytes directly instead of base64-encoded strings when
creating test data for XDRBytea fields.

Use raw bytes directly for test XDR data instead of base64-encoding.
The String() method will handle base64 encoding for assertions.

Use raw bytes directly instead of pre-encoded base64 string.

Use parameterized queries instead of raw SQL string literals
for BYTEA operation_xdr column. Fix .String() assertion to
compare base64 values via opXdr1.String().

Use parameterized queries instead of raw SQL string literals
for BYTEA operation_xdr column in BatchGetByOperationIDs and
BatchGetByStateChangeIDs tests.

Use parameterized queries instead of raw SQL string literals
for BYTEA operation_xdr column in BatchGetByOperationIDs test.

Copy the byte slice from the database driver instead of
referencing it directly. The pgx driver reuses its internal
buffer across rows, so without copying, all scanned XDRBytea
values end up pointing to the same (overwritten) buffer.