refactor(agent): reduce number of segments created

[zsistla]

Instead of a blanket segment_start in the "before" function that needs to be discarded in the majority of the cases, just create the segment when it is needed, add the attributes/metrics, then close the segment.

DONE:Multiverse SQS exception tests need to be updated.
DONE:Needs additional testing against backend.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	❌	4/8 passing
SOAK	❌	70/72 passing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 78.02%. Comparing base (3d71d47) to head (da4253b).

Files with missing lines	Patch %	Lines
agent/lib_aws_sdk_php.c	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1011      +/-   ##
==========================================
+ Coverage   78.01%   78.02%   +0.01%     
==========================================
  Files         197      197              
  Lines       27422    27418       -4     
==========================================
  Hits        21392    21392              
+ Misses       6030     6026       -4     

Flag	Coverage Δ
agent-for-php-7.2	78.15% <ø> (ø)
agent-for-php-7.3	78.17% <ø> (ø)
agent-for-php-7.4	77.88% <ø> (ø)
agent-for-php-8.0	77.25% <ø> (ø)
agent-for-php-8.1	77.76% <0.00%> (+0.01%)	⬆️
agent-for-php-8.2	77.36% <0.00%> (+0.01%)	⬆️
agent-for-php-8.3	77.36% <0.00%> (+0.01%)	⬆️
agent-for-php-8.4	77.38% <0.00%> (+0.01%)	⬆️

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[zsistla]

Looks good: