Go SDK: Keep audit interceptors non-blocking on errors

[jeongukjae]

Ensure Go audit-mode interceptors remain non-blocking when validator or mutator invocation returns an error.

Motivation and Context

SEP says audit-mode interceptors MUST NOT block execution regardless of results. The Go SDK already avoided blocking on audit-mode validation findings, but validator/mutator handler or RPC errors could still abort unless FailOpen was set.

This change makes audit mode consistently non-blocking for invocation errors as well, matching the existing C# orchestrator behavior where isAudit || failOpen allows execution to continue.

How Has This Been Tested?

Added focused Go chain tests covering audit-mode validator and mutator errors.

Breaking Changes

None. This only relaxes audit-mode error handling to match SEP semantics.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

C# already treats audit-mode invocation failures as non-blocking. This aligns the Go chain behavior with that implementation and SEP audit-mode semantics.