Use wider diagnostic output in UI tests

[joshlf]

Motivation

• UI tests were intermittently showing truncation notes (long-type files) and spurious wrapping due to a narrow diagnostic width, causing brittle snapshots and extra noise.
• Making the runner request a much wider diagnostic width and matching COLUMNS produces full diagnostics and more stable/meaningful .stderr snapshots.

Description

• Increase the --diagnostic-width argument from 100 to 1000 in tools/ui-runner/src/main.rs and anneal/tests/ui.rs so rustc emits wider, less-truncated diagnostics.
• Update the COLUMNS environment variable in tools/ui-runner to 1000 to match the requested diagnostic width.
• Re-bless numerous UI .stderr snapshots in zerocopy/tests/ui/ (stable and nightly variants) to remove /long-type-HASH.txt truncation notes and reflect wider source spans.

Testing

• Ran CARGO_ZEROCOPY_AUTO_INSTALL_TOOLCHAIN=1 BLESS=1 ./cargo.sh +stable test --test ui -p zerocopy --features=__internal_use_only_features_that_work_on_stable and the UI tests completed successfully.
• Ran CARGO_ZEROCOPY_AUTO_INSTALL_TOOLCHAIN=1 BLESS=1 ./cargo.sh +nightly test --test ui -p zerocopy --all-features and the UI tests completed successfully.
• Ran CARGO_ZEROCOPY_AUTO_INSTALL_TOOLCHAIN=1 BLESS=1 ./cargo.sh +msrv test --test ui -p zerocopy --features=__internal_use_only_features_that_work_on_stable and the UI tests completed successfully.
• Attempted the full snapshot update script ../tools/update-expected-test-output.sh, but it failed early because cargo-asm was not available in this environment and that prevented the codegen step from completing.

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Codex Task

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.85%. Comparing base (d35c00e) to head (0999137).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3461   +/-   ##
=======================================
  Coverage   91.85%   91.85%           
=======================================
  Files          20       20           
  Lines        6093     6093           
=======================================
  Hits         5597     5597           
  Misses        496      496           

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