chore: adopt assert_matches! in tests once it reaches stable

[acgetchell]

Summary

Adopt the standard‑library assert_matches! / debug_assert_matches! macros in unit and integration tests once they actually reach a stable Rust release.

Background

Issue #324 (MSRV bump to Rust 1.95) listed this task:

Replace manual pattern‑matching assertions in tests with assert_matches!

The stabilization PR (rust‑lang/rust#137487, "Stabilize assert_matches") was tagged milestone 1.95.0, but did not actually ship stable in rustc 1.95.0. The shipped library source for the 1.95.0 toolchain still carries:

#[unstable(feature = "assert_matches", issue = "82775")]
#[allow_internal_unstable(panic_internals)]
#[rustc_macro_transparency = "semiopaque"]
pub macro assert_matches { ... }

In the same file, cfg_select! did ship stable (#[stable(feature = "cfg_select", since = "1.95.0")]), confirming this is an assert_matches!‑specific slip, not a toolchain packaging issue.

Upstream tracking issue: rust‑lang/rust#82775.

Scope

Once assert_matches! lands on a stable release and our MSRV reaches that release, convert the 228 existing assert!(matches!(...)) call sites across the codebase:

• Integration tests (3 files, ~13 sites)
  • tests/large_scale_debug.rs
  • tests/insert_with_statistics.rs
  • tests/tds_orientation.rs
• Unit tests in src/ (28 files, ~215 sites); highest‑density:
  • src/core/tds.rs (~45)
  • src/core/triangulation.rs (~32)
  • src/core/algorithms/locate.rs (~16)
  • src/geometry/util/conversions.rs (~13)
  • src/core/algorithms/flips.rs (~12)
  • src/topology/traits/global_topology_model.rs (~11)

The mechanical transformation is:

// before
assert!(matches!(expr, Pat));
assert!(matches!(expr, Pat), "msg {ctx}");
assert!(matches!(expr, Pat { x, .. } if x > 0));

// after
assert_matches!(expr, Pat);
assert_matches!(expr, Pat, "msg {ctx}");
assert_matches!(expr, Pat { x, .. } if x > 0);

Import path (per 1.95 beta/stable docs once it lands):

use std::assert_matches;

Cases to leave alone (no direct replacement):

• assert!(!matches!(...)) — no assert_not_matches! exists; keep as‑is.
• Occurrences inside doc comments — keep aligned with whichever form the code uses at that time.

Tasks

• Confirm which stable release actually stabilizes assert_matches! / debug_assert_matches!
• Bump MSRV (separate issue) to that release
• Sweep integration tests in tests/
• Sweep unit tests in src/
• Run just ci to verify
• Close out the corresponding bullet in chore: update MSRV to Rust 1.95.0 #324

References

• chore: update MSRV to Rust 1.95.0 #324 — MSRV bump to Rust 1.95.0
• rust‑lang/rust#82775 — tracking issue
• rust‑lang/rust#137487 — stabilization PR (milestone 1.95.0; did not land in 1.95.0 stable)