fix: reject non-NGINX processes, classify nginx master by cmdline role instead of PPID

[ShubhenduSinghF5]

EnvironmentType.Processes() inferred IsMaster by checking whether a candidate nginx process's PPID was itself in the discovered nginx-process set — any nginx-named process whose parent was not another nginx process was flagged as a master.

This breaks when another tool injects a helper process that borrows the nginx: cmdline convention and runs under PID 1. A concrete case observed in the field: Dynatrace OneAgent injects a [nginx: OneAgent companion process] (name nginx, ppid 1), which the PPID heuristic classifies as a second master. Downstream, UpdateNginxDetailsFromProcesses keys nginxDetailsMap by the derived nginxId, both "masters" collide on the same key, and Go's non-deterministic map iteration decides which PID the agent sends the reload SIGHUP to. When the impostor wins, nginx -s reload silently no-ops while the agent still reports success.

Align v2's nginx master-process classification with the approach already used in NGINX Agent v3 [pkg/nginxprocess.Process.IsMaster] identify the master by the nginx-reported role prefix on the process command line rather than by parent-PID inference.

Proposed changes

Add [isNginxMaster(cmd string) bool] — mirrors the v3 implementation, checks for the nginx: master / {nginx-debug} nginx: master cmdline prefix.
Use it in Processes() in place of the PPID-based inference.
[isNginxProcess] (the collection filter) is unchanged; only role classification moves from PPID to cmdline.

Checklist

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• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

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[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (dev-v2@be022db). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/core/environment.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             dev-v2    #1837   +/-   ##
=========================================
  Coverage          ?   52.33%           
=========================================
  Files             ?       51           
  Lines             ?     3518           
  Branches          ?        0           
=========================================
  Hits              ?     1841           
  Misses            ?     1531           
  Partials          ?      146           

Files with missing lines	Coverage Δ
src/core/environment.go	57.36% <75.00%> (ø)

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[ShubhenduSinghF5]

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