[VEN-1895] Add Arbitrum sequencer downtime validation for Chainlink Oracle

[0xlucian]

Description

This PR adds Chainlink Oracle support for Arbitrum.

Resolves #VEN-1895

Checklist

• I have updated the documentation to account for the changes in the code.
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a test preventing this bug from silently reappearing again.
• My contribution follows Venus contribution guidelines.

[web3rover]

@0xlucian Instead of creating a separate contract I think we can add a sequencerUptimeFeed immutable address. If it's not zero then verify the sequencer uptime. I think this way we don't need to maintain multiple chainlink oracle contracts.

Also sequencer is used in OP, ARB and Base networks. So if we decide to use a separate contract, then we should rename the contract from ArbiChainlinkOracle to SequencerChainlinkOracle

[chechu]

@0xlucian Instead of creating a separate contract I think we can add a sequencerUptimeFeed immutable address. If it's not zero then verify the sequencer uptime. I think this way we don't need to maintain multiple chainlink oracle contracts.

Also sequencer is used in OP, ARB and Base networks. So if we decide to use a separate contract, then we should rename the contract from ArbiChainlinkOracle to SequencerChainlinkOracle

I would rename the contract to SequencerChainlinkOracle. I would personally keep it in its own contract, to avoid deploying code to networks that we won't use it

[0xlucian]

@chechu @Narayanprusty I think that having different oracle that extends this functionality makes more sense.. On one side it will save us gas on Ethereum (because we will not have this logic at all) and on the other side I think having non-zero address logic is kinda prone to more errors.
Maybe I can just rename the oracle for L2ChainlinkOracle or SequencerChainlinkOracle as proposed by @chechu . What do you think?

[web3rover]

I prefer SequencerChainlinkOracle as all L2s don't use a sequencer or need sequencer uptime validation.

[0xlucian]

@chechu @Narayanprusty ArbiChainlinkOracle has been renamed to SequencerChainlinkOracle. Let me know if I can merge this PR?

[kkirka]

LGTM overall

[github-actions]

Package	Line Rate	Branch Rate	Health
contracts	85%	80%	✔
contracts.interfaces	28%	21%	❌
contracts.oracles	96%	83%	✔
Summary	86% (233 / 270)	77% (132 / 172)	✔