refactor: make rt metric more performance and easy to use

[FoghostCn]

1. optimize rt calculation time
   The current implementation rt will be calculated every time the sample data is added, which is performance-intensive and unnecessary.
   new implementation will only be calculated when Prometheus pulls data

2. add more unit tests for metrics

3. add Rt interface to MetricRegisrty simplfy rt processing

for example:

var MetricRegisrty registry
registry.Rt(&MetricId{Name:"dubbo_request_rt", Desc: "Request RT"}).Observe(100)

// next time also call it in this way, no need to manually cache it
registry.Rt(&MetricId{Name:"dubbo_request_rt", Desc: "Request RT"}).Observe(100)

it will produce 5 metrics in prometheus:

# HELP dubbo_request_rt_avg Average request RT
# TYPE dubbo_request_rt_avg gauge
dubbo_request_rt_avg{app="dubbo",version="1.0.0"} 45
# HELP dubbo_request_rt_last Last request RT
# TYPE dubbo_request_rt_last gauge
dubbo_request_rt_last{app="dubbo",version="1.0.0"} 90
# HELP dubbo_request_rt_max Max request RT
# TYPE dubbo_request_rt_max gauge
dubbo_request_rt_max{app="dubbo",version="1.0.0"} 90
# HELP dubbo_request_rt_min Min request RT
# TYPE dubbo_request_rt_min gauge
dubbo_request_rt_min{app="dubbo",version="1.0.0"} 0
# HELP dubbo_request_rt_sum Sum request RT
# TYPE dubbo_request_rt_sum gauge
dubbo_request_rt_sum{app="dubbo",version="1.0.0"} 450

[codecov-commenter]

Codecov Report

Merging #2376 (32fb9d6) into main (8b43135) will increase coverage by 0.73%.
Report is 2 commits behind head on main.
The diff coverage is 95.03%.

@@            Coverage Diff             @@
##             main    #2376      +/-   ##
==========================================
+ Coverage   44.27%   45.00%   +0.73%     
==========================================
  Files         304      306       +2     
  Lines       18528    18687     +159     
==========================================
+ Hits         8203     8410     +207     
+ Misses       9467     9404      -63     
- Partials      858      873      +15     

Files Changed	Coverage Δ
common/host_util.go	85.18% <ø> (+14.81%)	⬆️
metrics/api.go	0.00% <0.00%> (ø)
metrics/prometheus/reporter.go	77.14% <ø> (ø)
metrics/prometheus/util.go	100.00% <ø> (ø)
metrics/prometheus/registry.go	88.88% <97.77%> (+87.71%)	⬆️
metrics/prometheus/rt_vec.go	100.00% <100.00%> (ø)
metrics/util/aggregate/aggregator.go	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[ev1lQuark]

LGTM

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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