fix(agent): don't try to instrument anything when not recording

[lavarou]

When agent is not recording, Observer API fcall_init callback shouldn't do anything, including framework detection. This is how the agent operated before it used Observer API to hook into Zend Engine.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	16/16 passing
SOAK	✅	85/85 passing

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.11%. Comparing base (2f79c48) to head (9c935fa).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1112      +/-   ##
==========================================
- Coverage   78.12%   78.11%   -0.01%     
==========================================
  Files         193      193              
  Lines       27989    27991       +2     
==========================================
  Hits        21866    21866              
- Misses       6123     6125       +2     

Flag	Coverage Δ
agent-for-php-7.2	78.37% <ø> (ø)
agent-for-php-7.3	78.38% <ø> (ø)
agent-for-php-7.4	78.24% <ø> (ø)
agent-for-php-8.0	77.44% <100.00%> (-0.01%)	⬇️
agent-for-php-8.1	77.76% <100.00%> (-0.01%)	⬇️
agent-for-php-8.2	77.37% <100.00%> (-0.01%)	⬇️
agent-for-php-8.3	77.37% <100.00%> (-0.01%)	⬇️
agent-for-php-8.4	77.39% <100.00%> (-0.01%)	⬇️

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