pg qrep: avro schema nullable by default

[serprex]

despite our efforts, nulled values still frequently leak through. put behind setting

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
1253	2	1251	128

View the full list of 2 ❄️ flaky test(s)

github.com/PeerDB-io/peerdb/flow/e2e::TestApiPg

Flake rate in main: 46.67% (Passed 16 times, Failed 14 times)

Stack Traces | 0.01s run time

=== RUN   TestApiPg
=== PAUSE TestApiPg
=== CONT  TestApiPg
--- FAIL: TestApiPg (0.01s)

github.com/PeerDB-io/peerdb/flow/e2e::TestApiPg/TestFlowStatusUpdate

Flake rate in main: 46.67% (Passed 16 times, Failed 14 times)

Stack Traces | 141s run time

=== RUN   TestApiPg/TestFlowStatusUpdate
=== PAUSE TestApiPg/TestFlowStatusUpdate
=== CONT  TestApiPg/TestFlowStatusUpdate
2025/10/16 20:18:14 INFO fetched schema x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN} table=e2e_test_mychcl_2hmx7yvo.test_nullengine
    flow_status_test.go:134: WaitFor wait for paused state 2025-10-16 20:18:18.821020432 +0000 UTC m=+265.914762732
    flow_status_test.go:144: WaitFor wait for running state 2025-10-16 20:18:34.843753164 +0000 UTC m=+281.937495474
2025/10/16 20:18:34 INFO fetched schema x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN} table=e2e_test_mychcl_2hmx7yvo.test_nullengine
    api_test.go:44: begin tearing down postgres schema api_22pfid5x
2025/10/16 20:18:35 INFO fetched schema x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN} table=e2e_test_mychcl_2hmx7yvo.test_nullengine
    api_test.go:44: 
        	Error Trace:	.../flow/e2e/pg.go:149
        	            				.../flow/e2e/api_test.go:44
        	            				.../flow/e2eshared/e2eshared.go:38
        	            				.../hostedtoolcache/go/1.25.2.../src/testing/testing.go:1308
        	            				.../hostedtoolcache/go/1.25.2.../src/testing/testing.go:1572
        	            				.../hostedtoolcache/go/1.25.2.../src/testing/testing.go:1928
        	            				.../hostedtoolcache/go/1.25.2.../src/runtime/asm_amd64.s:1693
        	Error:      	failed to teardown postgres schema
        	Test:       	TestApiPg/TestFlowStatusUpdate
        	Messages:   	api_22pfid5x: failed to drop e2e_test schema: timeout: context already done: context deadline exceeded
--- FAIL: TestApiPg/TestFlowStatusUpdate (141.26s)

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[ilidemi]

Logic LGTM. Please add test with and without the flag