feat(solana-wallet-snap): add batch proof-of-ownership signing

[hmalik88]

Explanation

Adds signProofOfOwnershipBatch to the Solana snap so MetaMask can request proof-of-ownership signatures for multiple accounts in one snap call.
The batch path:

• resolves requested accounts with one account lookup instead of one lookup per item
• validates proof messages per item
• returns per-item success/error results so one bad account or message does not fail the whole batch
• groups signing by entropySource
• fetches the Solana coin-type node (m/44'/501') once per entropy source
• derives account keys locally from the coin-type node before signing

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them