Instrument the block production and publishing code paths using tracing spans to enable end-to-end visibility and to improve debugging and performance analysis.

• Instrument block production in the beacon node
  • Instrument tracing on block production code path #8017
• Instrument block publishing in the beacon node
  • Instrument publish_block code path  #7945
• Instrument block proposal in validator client
• Propagate trace context between VC <> BN to maintain a single end-to-end trace

Note: the above tasks can be broken down into separate PRs if it's too big.