refactor: debugbar time header not dependent on locale

[michalsn]

Description
The U.u format is already providing us the correct format (6-digits). And with sprintf, the comma separator may be transformed either to . or , depending on locale (LC_NUMERIC).

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

Is there a downside to just using the capital F specifier?

[michalsn]

Yes, you're right - updated.

[neznaika0]

A microtime() is being used, yes, these are tests, I'll just note

CodeIgniter4/tests/system/Debug/Toolbar/Collectors/HistoryTest.php

Line 37 in 11f0130

$this->time = (float) sprintf('%.6f', microtime(true));

CodeIgniter4/tests/system/Debug/Toolbar/Collectors/HistoryTest.php

Line 66 in 11f0130

$path = str_replace((string) $time, sprintf('%.6f', $time - self::STEP), $path);

[michalsn]

Microtime is not a problem in this case, as it's only used to generate historical entries, but I updated formatting - thanks.

[michalsn]

Thank you everyone for the suggestions.