Move span errors to finish

[ChiragAgg5k]

Summary

• Move terminal span error capture into Span::finish(?Throwable $error = null)
• Remove the confusing static Span::error() helper
• Update tests and README guidance to distinguish error attributes from span failure

Testing

• composer test
• composer format
• vendor/bin/phpstan analyze --memory-limit=512M

[greptile-apps]

Greptile Summary

This PR consolidates span error capture into finish(?string $level = null, ?Throwable $error = null), removes the Span::error() static helper, and changes level to always be written at finish time rather than only when not already set. The README and tests are updated accordingly, and declare(strict_types=1) is added across all source and test files.

Confidence Score: 5/5

Safe to merge — no logic bugs found; all behavioural changes are intentional and well-tested.

No P0 or P1 issues found. The two breaking changes (removal of Span::error() and finish() now always overwriting level) are deliberately introduced, covered by tests, and documented in the README. All other changes are additive or housekeeping.

No files require special attention.

Important Files Changed

Filename	Overview
src/Span/Span.php	Removes Span::error(), extends finish() with $level/$error params, and changes level to always be set at finish time (no longer preserving pre-set values).
tests/SpanTest.php	Replaces old Span::error() tests with finish(error:) equivalents; adds testFinishOwnsLevelAttribute confirming the new always-overwrite level behaviour.
README.md	Updated error-handling guidance to use finish(error: $e), removed Span::error() from static-method table, and added prose about setError() for pre-finish error recording.
src/Span/Exporter/Exporter.php	Added declare(strict_types=1) only; no logic change.
src/Span/Exporter/Stdout.php	Added declare(strict_types=1) only; no logic change.
src/Span/Storage/Memory.php	Added declare(strict_types=1) only; no logic change.
src/Span/Storage/Coroutine.php	Added declare(strict_types=1) only; no logic change.

_{Reviews (6): Last reviewed commit: "Fix finish error parameter docs" | Re-trigger Greptile}