perf: Reduce allocations when creating metric families

[fpetkovski]

What this PR does / why we need it:

The metric family generates a series by using a strings.Builder to write data into, and then converts the string into a byte slice. This causes extra allocations which are not needed since we can directly write into a byte slice.

Benchmarks in CI show an improvement: https://github.com/kubernetes/kube-state-metrics/actions/runs/19236033135?pr=2807.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
Has no effect.

Which issue(s) this PR fixes: (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged)
Fixes #

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