feat: add minimum required version metric.

[qedgardo]

Summary

Add new metric solana_min_required_version to track the minimum required
Solana version for foundation delegation program across different clusters.

Details

• New metric solana_min_required_version with version and cluster labels
• New api package to handle non-RPC API calls
• Caching mechanism to reduce API calls (6-hour cache)
• Automatic cluster detection using genesis hash

Technical Details

• The metric queries https://api.solana.org/api/validators/epoch-stats to fetch the minimum version requirement
• Cluster is automatically determined from RPC endpoint's genesis hash:
  • Mainnet: 5eykt4UsFv8P8NJdTREpY1vzqKqZKvdpKuc147dw2N9d
  • Testnet: 4uhcVJyU9pJkvQyS88uRDiswHXSCkY3zQawwpjk2NsNY
  • Devnet: EtWTRABZaYq6iMfeYKouRu166VU2xqa1wcaWoxPkrZBG
• API responses are cached for 6 hours to minimize external calls

Testing

• Added unit tests for API client and caching behavior
• Added integration tests for metric collection
• Added mock clients for testing

[andreclaro]

solana-exporter only needs to query the SFDP API once a day or max every 6 or 12 hours (max).

[andreclaro]

Add unit tests :)

[Alex99y]

LGTM!

[johnstonematt]

I know it looks like I left a lot of issues, but they are generally all minor things. All round, I think this is a nice PR and I think you guys did a great job of introducing a whole new dimension to the exporter.

Please just address my (albeit generally minor) concerns and then once we are on the same page about those things I'll be happy to approve and merge.

[johnstonematt]

Hey, thanks for addressing the requests. I believe they were at all satisfied, but there are a few more concerns here. But overall, still nice stuff and thank you very much for the contribution so far already