chore(integritee): remove stale dormant func and tests

[shariqahmed-cohere]

There is a lot of legacy stale files and tests in this repo that are dormant but misleading. Trimming it to only keep the functionality we want and can test at this time, allowing for cleaner addition of trustee/amd features.

---

Note

Medium Risk
Drops the published Python client and large test coverage for removed scripts, which is a breaking change for any consumer still on the old per-model release layout; runtime policy actions are unchanged but attestation discovery docs now describe a different contract.

Overview
Removes dormant per-model scaffolding in favor of the current manifest-based release-policy flow. The entire clients/python package (IntegriteeClient and its tests) is deleted, along with tests and fixtures for legacy scripts/ (build-predicate, generate-ita-policy, merge-policy-inputs), end-to-end pipeline harnesses, and repo-layout checks for old models/ and attest-model workflows.

CI and packaging are simplified: Dependabot no longer tracks clients/python, install is only pip install -e ".[dev]", compileall skips removed paths, and pytest runs the full tests/ tree instead of a hand-picked subset. Dev deps drop jsonschema; firmware fetch tests move from test_policy_actions.py into test_generate_policy.py, which also gains coverage that static TDX platform fields stay in tdx_base_checks only.

README is rewritten for operators and auditors: TNG should use attestation-bundle.sigstore.json and read policy_id from the verified predicate; releases are described as repo-root artifacts (attestation-policy.rego, manifest bundle, single predicate) rather than {model}/ trees.

^{Reviewed by Cursor Bugbot for commit 562c58c. Bugbot is set up for automated code reviews on this repo. Configure here.}