feat: add CLI flag support to builder config

[7suyash7]

Implement #303 to add CLI flag support to override config.toml values. This allows operators to quickly modify configuration without editing the config file.

Changes

• Add CLI Flag support
• All config values (except el_node_ipc_path, waiting for Make IPC Path optional #314 to land), can be overridden via flags.
• Secret keys remain config/env only.
• Added a few tests and help text for all flags.

Example usage

Basic override:

cargo run --bin rbuilder run config.toml --log-json false --log-level debug

Multiple overrides:

cargo run --bin rbuilder run config.toml \
  --log-json false \
  --log-level debug \
  --full-telemetry-server-port 7500 \
  --dry-run true \
  --max-concurrent-seals 2

✅ I have completed the following steps:

• [✅] Run make lint
• [✅] Run make test
• [✅] Added tests (if applicable)