fix(decoderbufs): default op to INSERT for protobufjs 8.2+ compatibility

[kibae]

Problem

Upgrading protobufjs from 8.0.x to 8.2.0 (#179) broke decoder-decoderbufs.spec.ts:

FAIL src/test/decoder-decoderbufs.spec.ts
  decoderbufs › Insert, Delete(w/FK)
    Expected: 5
    Received: 0

Root cause

The Postgres decoderbufs output plugin (the C extension) omits the op field on the wire for INSERT events to save bytes (the value would be 0, which is the proto3 implicit default).

• protobufjs 8.0.x: A missing enum field on a proto2 message decoded to 0. We happened to read op === 0 and treated it as INSERT.
• protobufjs 8.2.0: Fixed proto2 enum default behavior to follow the spec — a missing enum field now decodes to the first declared value.

Our enum starts with UNKNOWN = -1:

Op: { values: { UNKNOWN: -1, INSERT: 0, UPDATE: 1, DELETE: 2, BEGIN: 3, COMMIT: 4 } }

So after 8.2.0, INSERT events arrive as op = -1 (UNKNOWN) and never match ProtocolBuffersOperation.INSERT.

Fix

Add an explicit "default": "INSERT" to the op field so messages without an op on the wire decode as INSERT(0). This matches the wire-format intent of postgres-decoderbufs and works on both 8.0.x and 8.2.0.

Verification

With protobufjs@8.2.0 and PG 17:

PASS src/test/decoder-decoderbufs.spec.ts
  decoderbufs
    ✓ Insert, Delete(w/FK) (1671 ms)
    ✓ Update (1120 ms)

Test Suites: 6 passed, 6 total
Tests:       16 passed, 16 total

Related

Unblocks #179 (bump protobufjs from 8.0.1 to 8.2.0).

[kibae]

Closing — this was a workaround for what turned out to be an upstream protobufjs 8.2.0 regression (see #179). The right fix is to wait for an upstream patch rather than papering over it in our proto definition. Will file a protobufjs issue separately.