feat: refactor log formats

[ltitanb]

follow up of #254, fix for #225

• make logging more predictable, and add more information in each log line. I also removed nested spans to make parsing json logs easier. Now each request has a single span, with a method field and optionally more information (depending on the call).
• refactor the [logs] section of the config

For pasing, JSON format should be used, which has a span field.
get_header

{"timestamp":"2025-03-19T18:31:21.086988Z","level":"INFO","ua":"","ms_into_slot":46506681086,"span":{"method":"/eth/v1/builder/header/{slot}/{parent_hash}/{pubkey}","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"5c8c6604-6400-4757-b6a3-00e2a32ca2a4","slot":0,"validator":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","name":""}}
{"timestamp":"2025-03-19T18:31:21.087032Z","level":"DEBUG","message":"using default config","relays":1,"pubkey":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","span":{"method":"/eth/v1/builder/header/{slot}/{parent_hash}/{pubkey}","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"5c8c6604-6400-4757-b6a3-00e2a32ca2a4","slot":0,"validator":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","name":""}}
{"timestamp":"2025-03-19T18:31:21.088663Z","level":"DEBUG","message":"received new header","relay_id":"mock_3201","latency":"1.336617ms","version":"deneb","value_eth":"0.000000000000000010","block_hash":"0x0100000000000000000000000000000000000000000000000000000000000000","span":{"method":"/eth/v1/builder/header/{slot}/{parent_hash}/{pubkey}","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"5c8c6604-6400-4757-b6a3-00e2a32ca2a4","slot":0,"validator":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","name":""}}
{"timestamp":"2025-03-19T18:31:21.090516Z","level":"INFO","message":"received header","value_eth":"0.000000000000000010","block_hash":"0x0100000000000000000000000000000000000000000000000000000000000000","span":{"method":"/eth/v1/builder/header/{slot}/{parent_hash}/{pubkey}","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"5c8c6604-6400-4757-b6a3-00e2a32ca2a4","slot":0,"validator":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","name":""}}

get_payload

{"timestamp":"2025-03-19T18:46:20.850360Z","level":"INFO","ua":"","ms_into_slot":46507580850,"span":{"block_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","block_number":0,"method":"/eth/v1/builder/blinded_blocks","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"a206c8dd-cadd-4dcf-aa03-430a39bd68ce","slot":0,"name":""}}
{"timestamp":"2025-03-19T18:46:20.851189Z","level":"DEBUG","message":"received unblinded block","relay_id":"mock_3801","retry":0,"latency":"562.511µs","version":"deneb","block_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","span":{"block_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","block_number":0,"method":"/eth/v1/builder/blinded_blocks","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"a206c8dd-cadd-4dcf-aa03-430a39bd68ce","slot":0,"name":""}}
{"timestamp":"2025-03-19T18:46:20.851242Z","level":"INFO","message":"received unblinded block","span":{"block_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","block_number":0,"method":"/eth/v1/builder/blinded_blocks","parent_hash":"0x0000000000000000000000000000000000000000000000000000000000000000","req_id":"a206c8dd-cadd-4dcf-aa03-430a39bd68ce","slot":0,"name":""}}