feat: implement Solana chain module (#22)

[syutoutousai]

Summary

Implements the Solana chain module as requested in issue #22, adding support for Solana mainnet and devnet.

Changes

• Feature-gated Support: Added a solana feature flag to minimize dependency bloat. Enabling it adds solana-sdk, solana-client, and spl-token.
• Core Implementation: Created src/chains/solana.rs providing SolanaConnector for RPC operations and SolanaWallet for keypair management.
• Operations: Added support for
  • Wallet generation and import from base58
  • Native SOL balance checks and transfers
  • SPL Token transfers
• Registry Updates: Added Solana and SolanaDevnet variants to the Chain enum with appropriate metadata (RPCs, symbols, explorers).
• Examples & Docs: Updated examples/multi_chain.rs to demonstrate Solana usage and updated README.md.
• Testing: Added tests/solana_integration.rs for verifying core functionality against a local validator.

Closes #22

[abhicris]

Welcome to kcolbchain, @syutoutousai — glad you're here. 🌱

Here's what happens from this PR:

1. Our automated review looks for obvious issues (tests, secrets, size) within a couple of hours.
2. If it's clean and CI passes, we merge without back-and-forth.
3. If we need changes, we'll leave a specific comment — not a generic nit. Push another commit and we re-review.

While you wait:

• Run the repo's tests locally (see the repo README.md).
• Keep the PR scoped to one concern — bigger PRs land slower.
• Don't commit tokens or .env contents.

What happens after your first merge

• You're listed on https://kcolbchain.com/contributors/ (opt-out anytime via data/contributors-optout.txt).
• At 2+ merged PRs you're a Regular; at 5+ you're a Fellow — Fellows are the pool we invite first for paid research, partner-org gigs, and grant-funded work. Details: https://kcolbchain.com/docs/org-contribution-policy.html
• Looking for what to pick up next? https://kcolbchain.com/invitations/ lists open help-wanted / good-first-issue across every kcolbchain repo.

Thanks for writing the code. We're building this to last.

[abhicris]

🤖 Audit verdict: needs_human

Implementation code is benign and properly gated behind feature flags, but integration tests contain compilation errors that prevent CI from passing.

Risks flagged:

• Integration test compilation errors: balance(), transfer_sol(), and transfer_spl_token() are synchronous but tests call them with .await, causing test compilation failure

Audited by the kcolbchain PR pipeline. See pipeline docs.

[Pattermesh]

Your PR was selected as the winner for the Solana chain module — nice work on the SolanaConnector, wallet support, and SPL token integration!

One blocker before merge: there's an async/sync mismatch in the integration tests — .await is called on sync methods. Could you fix the method signatures (make them async fn) or adjust the test calls? Once that's resolved, we'll merge immediately.

Thank you!