arch: implement CheckConnectivity and update IEigenDAClient for enhanced resilience

[rdin777]

Overview This PR introduces a proactive Connectivity Guard to the EigenDAClient to address potential silent failures during initialization. By verifying network reachability to both Ethereum RPC and the EigenDA Disperser, we ensure that operators are alerted to configuration issues before starting active data dispersal.

Key Changes:

Interface Evolution: Added CheckConnectivity(ctx context.Context) error to the IEigenDAClient interface to standardize health checks across the SDK.

Proactive Validation: Implemented active handshake logic in CheckConnectivity that verifies the gRPC connection to the Disperser and the JSON-RPC connection to the Ethereum node.

Technical Debt: Partially addresses the TODO regarding client encapsulation and resilience mentioned in api/clients/client.go.

Architectural Motivation: Drawing from experience with Base and Optimism, this pattern prevents "blind" registrations where an operator appears active on-chain but cannot fulfill requests due to networking issues.

Security: All contributions are made from a 2FA-secured account.

[flnnhuman]

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[rdin777]

"Hi @maintainer! I've implemented the CheckConnectivity guard for IEigenDAClient to resolve the internal TODO and enhance network resilience. Ready for review and CI checks when you have a moment.".

[rdin777]

My apologies for the oversight with the inline comment. I've cleaned up the code and updated the branch. The core logic for the connectivity guard remains as described in the summary.