feat: #104 add log format environment

[sxwebdev]

Available to use custom logger format

• LOG_FORMAT=console // by default
• LOG_FORMAT=json

Console format (default):

2025-12-19T15:16:40+03:00 WRN internal/config/defaults.go:249 > no explicit rating function is specified, 'defaultLatencyPolicyFunc' will be used to calculate rating pid=32870
2025-12-19T15:16:40+03:00 INF cmd/nodecore/main.go:46 > the 'defaultLatencyPolicyFunc' default score function will be used to calculate rating pid=32870
2025-12-19T15:16:40+03:00 INF internal/upstreams/blocks/head.go:130 > starting an rpc head of upstream bsc-mainnet-2 with poll interval 1m0s pid=32870
2025-12-19T15:16:40+03:00 INF internal/upstreams/blocks/head.go:130 > starting an rpc head of upstream bsc-mainnet-1 with poll interval 1m0s pid=32870
2025-12-19T15:16:40+03:00 INF internal/upstreams/blocks/head.go:130 > starting an rpc head of upstream bsc-mainnet-3 with poll interval 1m0s pid=32870
2025-12-19T15:16:40+03:00 INF internal/upstreams/blocks/head.go:130 > starting an rpc head of upstream bsc-mainnet-4 with poll interval 1m0s pid=32870
2025-12-19T15:16:40+03:00 INF internal/rating/registry.go:76 > rating will be calculated every 10s pid=32870

JSON format:

{"level":"warn","time":"2025-12-19T15:28:13.084781+03:00","caller":"internal/config/defaults.go:236","message":"no explicit rating function is specified, 'defaultLatencyPolicyFunc' will be used to calculate rating"}
{"level":"info","time":"2025-12-19T15:28:13.089108+03:00","caller":"cmd/nodecore/main.go:46","message":"the 'defaultLatencyPolicyFunc' default score function will be used to calculate rating"}
{"level":"info","time":"2025-12-19T15:28:13.089328+03:00","caller":"internal/upstreams/blocks/head.go:130","message":"starting an rpc head of upstream bsc-mainnet-4 with poll interval 1m0s"}
{"level":"info","time":"2025-12-19T15:28:13.089344+03:00","caller":"internal/upstreams/blocks/head.go:130","message":"starting an rpc head of upstream bsc-mainnet-2 with poll interval 1m0s"}
{"level":"info","time":"2025-12-19T15:28:13.089334+03:00","caller":"internal/upstreams/blocks/head.go:130","message":"starting an rpc head of upstream bsc-mainnet-1 with poll interval 1m0s"}
{"level":"info","time":"2025-12-19T15:28:13.089344+03:00","caller":"internal/upstreams/blocks/head.go:130","message":"starting an rpc head of upstream bsc-mainnet-3 with poll interval 1m0s"}
{"level":"info","time":"2025-12-19T15:28:13.090022+03:00","caller":"internal/rating/registry.go:76","message":"rating will be calculated every 10s"}