chore: updated SDK to polkadot-stable2512-3

[Klapeyron]

Overview

This PR bumps Substrate / Polkadot SDK dependencies to polkadot-stable2512-3 (parity tag on polkadot-sdk) and applies the follow-on API changes required for that release. The goal is to stay aligned with upstream stable2512 and with the partner-chains stack (see partner-chains#28). Required for #1244

Runtime / API

• sp_api::Core: execute_block now takes <Block as BlockT>::LazyBlock instead of Block; the implementation forwards directly to Executive::execute_block, which expects a lazy block in this SDK version.
• sp_block_builder::BlockBuilder: check_inherents likewise takes LazyBlock; InherentData::check_extrinsics is called with that type.
• mmr::MmrApi: API version 3 adds generate_ancestry_proof on the runtime API (ancestry proof generation was removed from BeefyApi in this line). The runtime implements it by delegating to pallet_mmr::Pallet::generate_ancestry_proof, and the MmrApi impl is annotated with #[api_version(3)] to match upstream runtimes (e.g. Westend / node template).
• BeefyApi: generate_ancestry_proof is not implemented on BeefyApi anymore in stable2512-3; callers should use MmrApi::generate_ancestry_proof instead.
• Removed an unused Encode import in the runtime where it became redundant.

Node

• sc_service::SpawnTasksParams: new field tracing_execute_block (Option<Arc<dyn TracingExecuteBlock<_>>>). Set to None unless you wire up trace_block RPC tracing (matches upstream solochain / node CLI templates).

Tests / mocks

• pallet-version mock: impl sp_api::Core uses execute_block(_: <Block as BlockT>::LazyBlock) for the same Core API change.

📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

Please describe any additional testing aside from CI:

• Additional tests are provided (if possible)

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other:
• N/A

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