metrics, cmd/geth: change init-process of metrics

[holiman]

Alternative to #30781 .
This PR modifies how the metrics library handles Enabled: previously, the package init decided whether to serve real metrics or just dummy-types.
This has several drawbacks:

• During pkg init, we need to determine whether metrics are enabled or not. So we first hacked in a check if certain geth-specific commandline-flags were enabled. Then we added a similar check for geth-env-vars. Then we almost added a very elaborate check for toml-config-file, plus toml parsing.
• Using "real" types and dummy types interchangeably means that everything is hidden behind interfaces. This has a performance penalty, and also it just adds a lot of code.

This PR removes the interface stuff, uses concrete types, and allows for the setting of Enabled to happen later. It is still assumed that metrics.Enable() is invoked fairly early on.

The somewhat 'heavy' operations, such as ticking meters and exp-decay, now checks the enable-flag to prevent resource leak.

The change may be large, but it's mostly pretty trivial, and from the last time I gutted the metrics, I ensured that we have fairly good test coverage.

[holiman]

Runtime examples

Load (and enable) from conf:

$ go run ./cmd/geth --metrics --metrics.addr 0.0.0.0 dumpconfig > conf && go run ./cmd/geth --metrics --config conf -dev 2>&1 | grep metrics
INFO [11-27|06:56:21.987] Maximum peer count                       ETH=50 total=50
INFO [11-27|06:56:22.028] Set global gas cap                       cap=50,000,000
INFO [11-27|06:56:22.029] Initializing the KZG library             backend=gokzg
INFO [11-27|06:56:25.473] Enabling metrics collection
INFO [11-27|06:56:25.473] Enabling stand-alone metrics HTTP endpoint address=0.0.0.0:6060
INFO [11-27|06:56:25.473] Starting metrics server                  addr=http://0.0.0.0:6060/debug/metrics

Load from conf, but override with commandline

$ go run ./cmd/geth --metrics --metrics.addr 0.0.0.0 dumpconfig > conf && go run ./cmd/geth --config conf -dev --metrics.addr 1.1.1.1 2>&1 | grep metrics
INFO [11-27|06:57:09.251] Maximum peer count                       ETH=50 total=50
INFO [11-27|06:57:09.273] Set global gas cap                       cap=50,000,000
INFO [11-27|06:57:09.274] Initializing the KZG library             backend=gokzg
INFO [11-27|06:57:12.972] Enabling metrics collection
INFO [11-27|06:57:12.972] Enabling stand-alone metrics HTTP endpoint address=1.1.1.1:6060
INFO [11-27|06:57:12.972] Starting metrics server                  addr=http://1.1.1.1:6060/debug/metrics
ERROR[11-27|06:57:12.973] Failure in running metrics server        err="listen tcp 1.1.1.1:6060: bind: cannot assign requested address"

Load from conf, override to disable metrics

[user@work go-ethereum]$ go run ./cmd/geth --metrics --metrics.addr 0.0.0.0 dumpconfig > conf && go run ./cmd/geth --config conf -dev --metrics=false --metrics.addr 1.1.1.1 2>&1 | grep metrics
INFO [11-27|06:57:39.724] Maximum peer count                       ETH=50 total=50
INFO [11-27|06:57:39.741] Set global gas cap                       cap=50,000,000
INFO [11-27|06:57:39.742] Initializing the KZG library             backend=gokzg

[fjl]

I don't like that this was changed to be just an int64. It doesn't improve the implementation code (have to convert it at every use), and the internals are fully exposed.

It's OK to define a struct with only one field sometimes.

[holiman]

It was a bit inconsistent they way it is right now:

// StandardCounter is the standard implementation of a Counter and uses the
// sync/atomic package to manage a single int64 value.
type StandardCounter atomic.Int64

vs

// StandardGauge is the standard implementation of a Gauge and uses the
// sync/atomic package to manage a single int64 value.
type StandardGauge struct {
	value atomic.Int64
}

So I decided to just make them identical

[holiman]

Starting this on both 05 and 06 now. My first attempt failed, the config-check which was using the config now hit upon the previously unused fields in the defaultconfig:

	InfluxDBEndpoint: "http://localhost:8086",
	InfluxDBDatabase: "geth",
	InfluxDBUsername: "test",
	InfluxDBPassword: "test",
	InfluxDBTags:     "host=localhost",

	// influxdbv2-specific flags
	EnableInfluxDBV2:     false,
	InfluxDBToken:        "test",
	InfluxDBBucket:       "geth",

And thus croaked on a Fatal: Flags --influxdb.metrics.organization, --influxdb.metrics.token, --influxdb.metrics.bucket are only available for influxdb-v2. This is now fixed: conflicts are checked on the flags, not the final config.

From what I can tell at a glance, the charts seem to be working like before