Remove the unused identity-token path

No merchant uses it. Drops the gate option, its verifier and key cache,
the adapter gates, the agent-card extension and the discovery advertising,
and takes agentscore-py 2.8.0. Version 3.2.0.

Author: vvillait88

agentscore_commerce/__init__.py

@@ -25,7 +25,6 @@
     MppxComposeOutcome,
     PricingResult,
     SettleOutcome,
-    build_aip_trusted_issuers,
     format_pydantic_errors,
     get_identity_status,
     pricing_result,
@@ -60,7 +59,6 @@
     A2A_DEFAULT_TRANSPORT,
     A2A_PROTOCOL_VERSION,
     AGENTSCORE_UCP_CAPABILITY,
-    AIP_A2A_EXTENSION_URI,
     FIXABLE_DENIAL_REASONS,
     UCP_A2A_EXTENSION_URI,
     A2AAgentCard,
@@ -93,7 +91,6 @@
     UCPSigningKey,
     UCPVerificationError,
     VerifyWalletSignerResult,
-    aip_a2a_extension,
     build_a2a_agent_card,
     build_agent_memory_hint,
     build_contact_support_next_steps,
@@ -172,7 +169,6 @@
     "A2A_DEFAULT_TRANSPORT",
     "A2A_PROTOCOL_VERSION",
     "AGENTSCORE_UCP_CAPABILITY",
-    "AIP_A2A_EXTENSION_URI",
     "FIXABLE_DENIAL_REASONS",
     "UCP_A2A_EXTENSION_URI",
     "VERIFICATION_SESSION_HEADER",
@@ -243,10 +239,8 @@
     "WorkOutcome",
     "X402BaseRailSpec",
     "__version__",
-    "aip_a2a_extension",
     "build_a2a_agent_card",
     "build_agent_memory_hint",
-    "build_aip_trusted_issuers",
     "build_contact_support_next_steps",
     "build_default_checkout_rails",
     "build_gate_from_policy",