feat: implement gRPC connection with keepalive and retry interceptor

[mateeullahmalik]

Fixes permanent lumera connection failures on transient network errors by adding automatic retry with exponential backoff and keepalive configuration.

[Copilot]

Pull Request Overview

This PR implements gRPC connection improvements to handle transient network errors by adding automatic retry with exponential backoff and keepalive configuration to prevent permanent connection failures.

• Replaces direct gRPC dialing with a more robust connection mechanism featuring keepalive parameters
• Adds a retry interceptor with exponential backoff (2s → 4s → 8s → 16s → 30s capped) for failed calls
• Introduces comprehensive test coverage for connection normalization, retry logic, and edge cases

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pkg/lumera/connection.go	Implements gRPC connection with keepalive parameters and retry interceptor with exponential backoff
pkg/lumera/connection_test.go	Adds comprehensive test coverage for address normalization, connection methods, and retry behavior

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