fix: attempt all composed reporters

[favonia]

A failed Healthchecks request could short-circuit heartbeat composition and prevent a later Uptime Kuma update; the same aggregation pattern also affected composed notifiers. This change evaluates every applicable child before aggregating the results, so later reporters are still attempted while the overall result continues to report any failure. Focused regressions cover Ping, Start, Exit, Log, and Send, and the full Go suite and linter pass. Fixes #1248.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.49%. Comparing base (ec10e81) to head (1519d12).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1249   +/-   ##
=======================================
  Coverage   98.49%   98.49%           
=======================================
  Files         100      100           
  Lines        6249     6255    +6     
=======================================
+ Hits         6155     6161    +6     
  Misses         81       81           
  Partials       13       13           

Flag	Coverage Δ
smoketests	11.87% <27.27%> (-0.02%)	⬇️
unittests	98.11% <100.00%> (+<0.01%)	⬆️

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