Enable XDBG tests again

[mkysel]

Enable XDBG integration tests by adding container builders and wiring full end-to-end flow in integration_test.TestXDBGRealMLSPayloads

• Introduces reusable test container builders for Anvil (builders.AnvilContainerBuilder), xmtpd (builders.XmtpdContainerBuilder), xmtpd-gateway (builders.XmtpdGatewayContainerBuilder), xdbg (builders.XdbgContainerBuilder), and CLI (builders.CLIContainerBuilder) under xdbg_container_builder.go, xmtpd_container_builder.go, xmtp_gateway_container_builder.go, cli_container_builder.go, and anvil_container_builder.go

• Adds CLI-based builders.RegisterNode and builders.EnableNode flows to register and enable a node during tests in cli_commands.go

• Replaces skipped XDBG test with an end-to-end network bring-up and three generators (identity, group, message) with count 10 in xdbg_test.go

• Extracts common test utilities and constants into utils.go and centralizes the Anvil image in anvil.go

• Updates upgrade tests to use new builders in upgrade_test.go and removes in-test builder implementations from docker_utils_test.go

• Adds ignore patterns for integration artifacts in .dockerignore and exports XMTPD_SIGNER_ADDRESS in dev/local.env

📍Where to Start

Start with the test flow in TestXDBGRealMLSPayloads to see how the builders are composed in xdbg_test.go, then review the container builder implementations beginning with utils.go.

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Macroscope summarized b4f26c8.

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[fbac]

LGTM, very clean.