chore: Updated SDK to polkadot-stable2603

[Klapeyron]

Bump all Polkadot SDK dependencies from polkadot-stable2512-3 to polkadot-stable2603.

Release notes: polkadot-stable2603 (2512 → 2603)

Key upstream breaking changes addressed

• Proposer trait refactor (paritytech/polkadot-sdk#9947): Proposer::propose() now takes a single ProposeArgs<B> struct instead of individual parameters. The proof recorder is no longer initialised internally by BlockBuilder — it is passed in by the caller, moving responsibility for extracting the final storage proof outward. The ProofRecording and Proof associated types are removed from the Proposer trait.
• GrandpaPruningFilter (paritytech/polkadot-sdk#10893): new_full_parts now requires a block_pruning_filters parameter. Solochain nodes using GRANDPA must pass vec![Arc::new(GrandpaPruningFilter)] to preserve blocks with GRANDPA justifications needed for warp sync proofs. Without this, pruned nodes cannot serve warp sync proofs.
• Session key ownership proof (paritytech/polkadot-sdk#1739): generate_session_keys now takes an owner parameter and returns OpaqueGeneratedSessionKeys. This supports verifiable proof-of-ownership when registering session keys on chain, preventing key impersonation.
• RuntimeDebug deprecated (paritytech/polkadot-sdk#10582): sp_runtime::RuntimeDebug is deprecated in favour of plain Debug. Benchmarks showed the WASM size difference is negligible (~0.3% compressed), so the separate no-op-in-wasm derive is no longer justified.
• spawn_essential_handle: build_network params now requires a spawn_essential_handle field.

Changes in this PR

• Cargo.toml / Cargo.lock: Update all ~65 polkadot-sdk workspace dependency tags stable2512-3 → stable2603
• demo/node/src/service.rs:
  • Pass vec![Arc::new(GrandpaPruningFilter)] to both new_full_parts call sites
  • Add spawn_essential_handle to build_network params
• demo/runtime/src/lib.rs: Update generate_session_keys signature for ownership proof support
• substrate-extensions/aura/consensus/src/lib.rs: Adapt DummyProposer and test code to new ProposeArgs / Proposal types (remove ProofRecording, Proof, proof field)
• substrate-extensions/aura/primitives/src/block_proposal.rs: Adapt PartnerChainsProposer to destructure and forward ProposeArgs (including new storage_proof_recorder and extra_extensions fields)
• toolkit/block-participation/primitives/src/lib.rs: Replace sp_runtime::RuntimeDebug with Debug
• toolkit/block-production-log/primitives/src/lib.rs: Replace sp_runtime::RuntimeDebug with Debug
• toolkit/committee-selection/primitives/src/lib.rs: Replace sp_runtime::RuntimeDebug with Debug
• toolkit/sidechain/domain/src/mainchain_epoch.rs: Replace sp_core::RuntimeDebug with Debug
• README.md: Update SDK badge to stable2603
• changelog.md: Note the dependency bump

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• The size limit of 400 LOC isn't needlessly exceeded
• The PR refers to a JIRA ticket (if one exists)
• New tests are added if needed and existing tests are updated.
• New code is documented and existing documentation is updated.
• Relevant logging and metrics added
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff

[gilescope]

Can you use the https://github.com/paritytech/psvm tool to update it - that should be able to point us at the crate versions - these fetch faster than git references.