Fix Runtime API Discovery for PAPI

[oliverrigonan]

This PR resolves the issue related to PAPI (Polkadot API) runtime API discovery.

PAPI Runtime API Discovery

During integration testing with PAPI, runtime APIs were not being detected in the PAPI console, and downloading descriptors consistently failed. For example, when running the following command:

npx papi add xodePolkadot --wsUrl wss://polkadot-rpcnode.xode.net

The generated runtime API types were empty:

type IViewFns = {};
type IRuntimeCalls = {};

This issue was traced to changes in the Polkadot SDK (paritytech/polkadot-sdk#6665) where runtime API implementations were split into a dedicated api.rs file. While this worked within the SDK, it caused PAPI to fail in discovering and generating the runtime API types.

Fix: All runtime API implementations were moved back from api.rs into lib.rs. This change restored proper runtime API detection, and PAPI now successfully generates the expected IViewFns and IRuntimeCalls types.

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Issues Resolved

• Closes #90 — Track Xode Polkadot-API Runtime API Issues

Summary of Changes

• Moved runtime API implementations from api.rs back to lib.rs to fix PAPI runtime discovery.
• Fixed issue where PAPI runtime API types (IViewFns, IRuntimeCalls) were empty.
• Verified runtime API discovery functionality in the PAPI console.
• Ensured compatibility with existing runtime logic.

Impact

• Restores runtime API detection in PAPI, ensuring runtime API types are generated correctly.
• Aligns our runtime with the latest Polkadot SDK standards, while maintaining compatibility with PAPI.

[hgminerva]

Further explaination to the changes: polkadot-api/polkadot-api#1164