This PR replaces Geth's logger package (a fork of [log15](https://github.com/inconshreveable/log15)) with an implementation using slog, a logging library included as part of the Go standard library as of Go1.21.
Main changes are as follows:
* removes any log handlers that were unused in the Geth codebase.
* Json, logfmt, and terminal formatters are now slog handlers.
* Verbosity level constants are changed to match slog constant values. Internal translation is done to make this opaque to the user and backwards compatible with existing `--verbosity` and `--vmodule` options.
* `--log.backtraceat` and `--log.debug` are removed.
The external-facing API is largely the same as the existing Geth logger. Logger method signatures remain unchanged.
A small semantic difference is that a `Handler` can only be set once per `Logger` and not changed dynamically. This just means that a new logger must be instantiated every time the handler of the root logger is changed.
----
For users of the `go-ethereum/log` module. If you were using this module for your own project, you will need to change the initialization. If you previously did
```golang
log.Root().SetHandler(log.LvlFilterHandler(log.LvlInfo, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
```
You now instead need to do
```golang
log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelInfo, true)))
```
See more about reasoning here: https://github.com/ethereum/go-ethereum/issues/28558#issuecomment-1820606613
* internal/testlog: print file+line number of log call in test log
This changes the unit test logger to print the actual file and line
number of the logging call instead of "testlog.go:44".
Output of 'go test -v -run TestServerListen ./p2p' before this change:
=== RUN TestServerListen
--- PASS: TestServerListen (0.00s)
testlog.go:44: DEBUG[01-08|15:16:31.651] UDP listener up addr=127.0.0.1:62678
testlog.go:44: DEBUG[01-08|15:16:31.651] TCP listener up addr=127.0.0.1:62678
testlog.go:44: TRACE[01-08|15:16:31.652] Accepted connection addr=127.0.0.1:62679
And after:
=== RUN TestServerListen
--- PASS: TestServerListen (0.00s)
server.go:868: DEBUG[01-08|15:25:35.679] TCP listener up addr=127.0.0.1:62712
server.go:557: DEBUG[01-08|15:25:35.679] UDP listener up addr=127.0.0.1:62712
server.go:912: TRACE[01-08|15:25:35.680] Accepted connection addr=127.0.0.1:62713
* internal/testlog: document use of t.Helper
