Identify telemetry events when user identify is known

[safaricd]

Issue

With this PR, and only for identified usage - where users have accepted the license and created a Prior Labs account - we begin identifying telemetry events.

For anonymous events, we also drop recording fit_called and predict_called events.

Motivation and Context

Motivated by the recent gating changes where we switched from HuggingFace to model gating via ux.priorlabs.ai.

Public API Changes

• No Public API changes

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How Has This Been Tested?

Yes, manually and also with unit tests.

Checklist

• The changes have been tested locally.
• Documentation has been updated (if the public API or usage changes).
• A changelog entry has been added (see changelog/README.md), or "no changelog needed" label requested.
• The code follows the project's style guidelines.
• I have considered the impact of these changes on the public API.

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[gemini-code-assist]

Code Review

This pull request replaces the existing telemetry implementation with a new system in src/tabpfn/telemetry.py and adds pyjwt as a dependency. The review identifies several performance and architectural concerns: the _patch_client function configures a local instance that is not persisted, and ProductTelemetry is redundantly instantiated on every event capture. Furthermore, the Posthog client should utilize the api_host from the configuration, and the decoded user ID should be cached to prevent repeated JWT decoding overhead.

[dianaprior]

Some important comments re: correctness of telemetry file

[brendan-priorlabs]

Thanks for the PR, Dominik! Code seems clean. Left some small comments. Thank you @dianaprior as well for covering the README side of the review!

[brendan-priorlabs]

Oh and for the test failures, ImportError: cannot import name 'ModelLoadEvent' from 'tabpfn_common_utils.telemetry.core.events, do we just need a version bump on tabpfn_common_utils?

[brendan-priorlabs]

LGTM on the code side. Thanks, Dominik!

[brendan-priorlabs]

Sorry, withdrawing LGTM pending internal discussion :/