test: add shared conformance adapters and reports

[nkavian]

Summary

• Exercise public Python SDK calls with pinned shared runtime, MPP, and x402 fixtures.
• Generate reports on Python 3.11–3.14, including dependency versions and explicit unsupported-feature results.
• Document the adapter setup, local commands, and the existing Seller-subscription limitation.

Verification

• make sync and make verify passed on Python 3.11–3.14, including isolated consumer installation.
• Adapter orchestration tests passed.
• Shared reports passed all 82 runtime, 73 applicable MPP, and 77 x402 cases. The 10 unsupported MPP Seller-subscription cases are explicitly skipped.

No SDK runtime behavior or production dependencies change. Live payments and cross-SDK interoperability are separate verification tasks.