fix: prevent crash converting UUID timestamps near the Unix epoch

PhpTimeConverter::convertTime() threw an uncaught
InvalidArgumentException for v1/v6 UUID timestamps within about
100 microseconds of the Unix epoch (on the pre-1970 side), because
PHP renders such small floats in scientific notation, which
splitTime() misparsed as a malformed microseconds fragment.

splitTime() now recognizes scientific notation and defers to the
existing GenericTimeConverter fallback, the same mechanism already
used for other precision-loss cases.

src/Converter/Time/PhpTimeConverter.php

@@ -26,6 +26,7 @@ use function dechex;
 use function explode;
 use function is_float;
 use function is_int;
+use function str_contains;
 use function str_pad;
 use function strlen;
 use function substr;
@@ -142,6 +143,12 @@ class PhpTimeConverter implements TimeConverterInterface
             return ['sec' => $split[0], 'usec' => '0'];
         }
 
+        // Near zero PHP renders the float in scientific notation ("-1.0E-6"), whose
+        // exponent would be misparsed as microseconds; fall back instead.
+        if (str_contains($split[1], 'E')) {
+            return [];
+        }
+
         // If the microseconds are less than six characters AND the length of the number is greater than or equal to the
         // PHP precision, then it's possible that we lost some precision for the microseconds. Return an empty array so
         // that we can choose to use the fallback converter.

tests/Converter/Time/PhpTimeConverterTest.php

@@ -133,6 +133,14 @@ class PhpTimeConverterTest extends TestCase
                 'unixTimestamp' => '0',
                 'microseconds' => '0',
             ],
+
+            // One microsecond before the epoch: PHP renders "-1.0E-6", which must not
+            // be misparsed as microseconds.
+            [
+                'uuidTimestamp' => new Hexadecimal('1b21dd213813ff6'),
+                'unixTimestamp' => '0',
+                'microseconds' => '1',
+            ],
         ];
     }