Overhaul stats: Fix Prometheus export to include only one HELP and TYPE lines per metric

[josecelano]

Fix Prometheus export to include only one HELP and TYPE lines per metric.

Current format:

# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0087"} 4
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (FD66)",client_software_version=""} 1
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (SP)",client_software_version="3605"} 631
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (TIX0325)",client_software_version=""} 14
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0202"} 6754
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (XF)",client_software_version="9400"} 1
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0090"} 7
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Transmission",client_software_version="2.32"} 1
# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (61-b39e)",client_software_version=""} 1

Expected format:

# HELP udp_tracker_server_connection_id_errors_total Total number of requests with connection ID errors
# TYPE udp_tracker_server_connection_id_errors_total counter
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0087"} 4
udp_tracker_server_connection_id_errors_total{client_software_name="Other (FD66)",client_software_version=""} 1
udp_tracker_server_connection_id_errors_total{client_software_name="Other (SP)",client_software_version="3605"} 631
udp_tracker_server_connection_id_errors_total{client_software_name="Other (TIX0325)",client_software_version=""} 14
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0202"} 6754
udp_tracker_server_connection_id_errors_total{client_software_name="Other (XF)",client_software_version="9400"} 1
udp_tracker_server_connection_id_errors_total{client_software_name="Other (BC)",client_software_version="0090"} 7
udp_tracker_server_connection_id_errors_total{client_software_name="Transmission",client_software_version="2.32"} 1
udp_tracker_server_connection_id_errors_total{client_software_name="Other (61-b39e)",client_software_version=""} 1

A line break has also been added after each metric to improve readability.

[josecelano]

ACK 02433cb

[codecov]

Codecov Report

Attention: Patch coverage is 96.22642% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.85%. Comparing base (d7af961) to head (02433cb).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/metrics/src/label/set.rs	83.33%	1 Missing ⚠️
packages/metrics/src/sample.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1574      +/-   ##
===========================================
- Coverage    83.88%   83.85%   -0.03%     
===========================================
  Files          284      284              
  Lines        20333    20318      -15     
  Branches     20333    20318      -15     
===========================================
- Hits         17056    17038      -18     
- Misses        2976     2979       +3     
  Partials       301      301              

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