Fix(SDK): Auto root span start timestamps precision

[zigzagdev]

Summary

Content

Fixed a precision loss bug in AutoRootSpan::create() where the start timestamp was calculated incorrectly when REQUEST_TIME_FLOAT is not available.

Root Cause

The original code cast microtime(true) to int before multiplying via NANOS_PER_SECOND:

$startTime = array_key_exists('REQUEST_TIME_FLOAT', $request->getServerParams())
    ? $request->getServerParams()['REQUEST_TIME_FLOAT'] : (int) microtime(true);          // ← precision loss here
->setStartTimestamp((int) ($startTime * ClockInterface::NANOS_PER_SECOND))

This caused up to 999,999,999ns (~1 second) of error because the sub-second precision was discarded before nanosecond conversioning.

• GET /?foo=bar with microtime(true) = 1718123456.789 → cast to 1718123456 → multiplied by 1e9 → last 9 digits always 000000000

What I have done

Multiply first, then cast to int to preserve sub-second precision like:

$startTimeInNanos = array_key_exists('REQUEST_TIME_FLOAT', $request->getServerParams())
? (int) ($request->getServerParams()['REQUEST_TIME_FLOAT'] * ClockInterface::NANOS_PER_SECOND)
    : (int) (microtime(true) * ClockInterface::NANOS_PER_SECOND)
->setStartTimestamp($startTimeInNanos)

Test Results

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.92%. Comparing base (2f1c57f) to head (e912631).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1985      +/-   ##
============================================
+ Coverage     67.87%   67.92%   +0.04%     
  Complexity     3046     3046              
============================================
  Files           459      459              
  Lines          8891     8891              
============================================
+ Hits           6035     6039       +4     
+ Misses         2856     2852       -4     

Flag	Coverage Δ
8.1	67.64% <100.00%> (+0.06%)	⬆️
8.2	67.75% <100.00%> (-0.06%)	⬇️
8.3	67.73% <100.00%> (-0.08%)	⬇️
8.4	67.84% <100.00%> (+0.07%)	⬆️
8.5	67.75% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/SDK/Trace/AutoRootSpan.php	87.23% <100.00%> (+2.12%)	⬆️

... and 5 files with indirect coverage changes

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[ChrisLightfootWild]

Thanks for the PR @zigzagdev 💪