feat: better integration between llma and error tracking

[daibhin]

Problem

Inspired by this thread: https://posthog.slack.com/archives/C07AA937K9A/p1759356822031919

Changes

• Add LLMA trace_id (for starters, could add other properties too) to exceptions and set exception_id on trace events
• Add ability to Node SDK to skip previously captured exceptions (so we don't double capture)
• Remove unnecessary isError check given we have the error

Release info Sub-libraries affected

Libraries affected

• [ ] All of them
• [ ] posthog-js (web)
• [ ] posthog-js-lite (web lite)
• [x] posthog-node
• [ ] posthog-react-native
• [ ] @posthog/react
• [x] @posthog/ai
• [ ] @posthog/nextjs-config
• [ ] @posthog/nuxt