[fix][fn] Fix Go function runtime to continue after user exceptions and add neg-ack tests

[Dream95]

Motivation

Go function runtime currently exits the processing loop when user code returns an error, which causes behavior inconsistency with Java/Python runtimes and prevents expected retry/negative-ack flow in failure scenarios.
This PR aligns Go runtime behavior for user-function failures and adds integration coverage for Go neg-ack semantics.

This PR aligns Go runtime behavior for user-function failures and adds integration coverage for Go neg-ack semantics.

Modifications

• In pulsar-function-go/pf/instance.go:
  • Refactored error handling into helper methods (handleUserError, handlePublishError).
  • Changed user-function error path from returning error (exit loop) to continuing message processing.
  • Added shouldNackInputOnFailure() and enabled nack for ATLEAST_ONCE and MANUAL on user-function failures.
  • Kept publish-error handling with system exception metrics and appropriate ack/nack behavior.
• In pulsar-function-go/pf/instance_test.go:
  • Added Go exception function example: tests/docker-images/latest-version-image/go-examples/exceptionFunc/exceptionFunc.go.
  • Updated Docker image build to include the new Go example artifact.
  • Added testGoFunctionNegAck in Go integration test suite.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

./gradlew :tests:integration:integrationTest \
  -PintegrationTestSuiteFile=pulsar-process.xml \
  -PtestGroups=go_function

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Matching PR in forked repository

PR in forked repository: Dream95#10

[lhotari]

LGTM