refactor(agent): improve logging when adding named tracers

[lavarou]

Make log messages easier to understand when adding a named custom tracer by logging only a single message. Instead of logging one message when the wraprec is added, and two messages when wraprec is re-used, log a single message that indicates if the wraprec was added or re-used.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	8/8 passing
SOAK	❌	84/85 passing

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.25%. Comparing base (1099f17) to head (8bfd618).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1061      +/-   ##
==========================================
+ Coverage   77.08%   77.25%   +0.17%     
==========================================
  Files         198      199       +1     
  Lines       28126    28306     +180     
==========================================
+ Hits        21680    21869     +189     
+ Misses       6446     6437       -9     

Flag	Coverage Δ
agent-for-php-7.2	77.47% <100.00%> (+<0.01%)	⬆️
agent-for-php-7.3	77.49% <100.00%> (?)
agent-for-php-7.4	77.36% <100.00%> (?)
agent-for-php-8.0	76.56% <100.00%> (?)
agent-for-php-8.1	76.88% <100.00%> (+<0.01%)	⬆️
agent-for-php-8.2	76.50% <100.00%> (+<0.01%)	⬆️
agent-for-php-8.3	76.50% <100.00%> (?)
agent-for-php-8.4	?

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