[Feature Request] Update dimensions in Gauge/Meter/etc. a public var

[yeahdongcn]

Expected behavior

When collecting metrics for Prometheus, I found using previously declared Gauge/etc. was not convenient.
The following code snippet shows how I reuse the Gauge/etc. in Go:

type Collector struct {
	sync.Mutex
	usedMemory        *prometheus.GaugeVec
}

func (c *Collector) Collect(ch chan<- prometheus.Metric) {
	// Only one Collect call in progress at a time.
	c.Lock()
	defer c.Unlock()

	c.usedMemory.Reset()

	...
	for i := 0; i < int(numDevices); i++ {
		c.usedMemory.WithLabelValues(index, uuid, name, sn, slot).Set(float64(mem.Used))
	}
	...
}

I can reuse usedMemory for multiple devices and update the labels (similar to dimensions). But dimensions is a public let in Gauge/etc., I can't mutate its values.

Actual behavior

dimensions is a public let in Gauge/etc., I can't mutate its values after init.

Steps to reproduce

N/A

If possible, minimal yet complete reproducer code (or URL to code)

N/A

SwiftMetrics version/commit hash

2.4.1

Swift & OS version (output of swift --version && uname -a)

~ swift --version
swift-driver version: 1.62.15 Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51)
Target: arm64-apple-macosx13.0
~ uname -a
Darwin bogon 22.6.0 Darwin Kernel Version 22.6.0: Sun Dec 17 22:14:44 PST 2023; root:xnu-8796.141.3.703.2~2/RELEASE_ARM64_T8103 arm64