Restore full paths in span errors

[saulshanabrook]

Context

Span display was truncating paths to file names, which loses useful context when callers pass meaningful source paths.

Changes

• Preserves full caller-provided paths in Span display.
• Keeps file-test snapshots stable by passing file-name-only labels for fail-typecheck snapshot runs.
• Adds a span display regression test.

Validation

• cargo test -p egglog-ast egglog_span_display_preserves_full_path
• cargo test --test files arity_mismatch
• cargo fmt
• git diff --check

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.08%. Comparing base (e564e46) to head (90f111f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #886   +/-   ##
=======================================
  Coverage   87.08%   87.08%           
=======================================
  Files          88       88           
  Lines       25867    25873    +6     
=======================================
+ Hits        22526    22532    +6     
  Misses       3341     3341           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[codspeed-hq]

Merging this PR will improve performance by 27.39%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
❌ 1 regressed benchmark
✅ 22 untouched benchmarks
🆕 1 new benchmark
⏩ 215 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	tests[python_array_optimize]	1.5 s	1.7 s	-8.09%
🆕	Simulation	tests[repro-herbie-vanilla]	N/A	1.4 s	N/A
⚡	Simulation	rust_rule_fib[rule_run_1000]	280.7 ms	202.8 ms	+38.39%
⚡	Simulation	tests[cykjson]	440.2 ms	270.8 ms	+62.53%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing saulshanabrook:codex/split-span-full-path-errors (90f111f) with main (8c1c70b)²}

Footnotes

1. 215 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (e564e46) during the generation of this report, so 8c1c70b was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩