Move client_golang to v1.25.0 with its required module updates
(client_model v0.6.3, common v0.72.0, procfs v0.22.0, xxhash v2.3.0,
protobuf v1.36.12, munnerz/goautoneg). go.mod keeps go 1.26.0 and has
no toolchain line.
Sync the frpc text metrics clone with the new default Go collector:
add go_gc_gogc_percent, go_gc_gomemlimit_bytes and
go_sched_gomaxprocs_threads, update the go_memstats help texts, and
remove go_memstats_lookups_total. frpc still exposes go_* metrics only.
Add pkg/metrics/text, a small Prometheus text-format writer, and use it
for frpc's /metrics. The endpoint lives only on metricsServer and is
covered by its Basic Auth, like the other endpoints there.
The package emits the Go runtime families and, on Linux, the process
families read from /proc. Their names, types and help strings match
client_golang's default collectors, so existing Go runtime dashboards
keep working. It deliberately emits no frp_ business metrics and none of
client_golang's promhttp_ handler metrics.
Writing the subset ourselves keeps client_golang and protobuf out of the
frpc binary; both are still used by frps and by the tests here.
fatedier