Route Boolean3::Result timing through the shared phase mechanism

[zmerlynn]

Follow-up to #1742, addressing the review ask: reuse the new per-phase timing to drop Boolean's hand-placed Timers, for consistency.

Result's four Timers (Assembly/Triangulation/Simplification/Sorting) bracketed spans that were already unions of phase() boundaries, so the phase() lambda now records through the same path as the ADVANCE_PHASE_OR_RETURN ops, via a new explicit-line MANIFOLD_RECORD_PHASE_AT (a lambda called from 11 sites would otherwise report a single line). BeginPhaseTiming seeds the baseline at Result entry, since Boolean never hits the static-factory reset that seeds it for LevelSet/FromMesh/Smooth. perfPhases now drives its booleans through an ExecutionContext so the lines print.

Every phased op now emits the one phase N (file:line) = X ms format. The intersection-stage Timers are kept; the 11 phase lines replace the old four named Timers:

=== Sphere(32): subtract ===
----------- 0 ms for Intersect12 P->Q
----------- 0 ms for Intersections (total)
  phase 1 (boolean_result.cpp:772) = 0.0002 ms
  ...
  phase 11 (boolean_result.cpp:959) = 3.38 ms
366 verts and 728 tris

Notes:

• Kept the intersection-stage Timers in the Boolean3 ctor (Intersect12 P->Q / Q->P, Winding03 P / Q): a P/Q sub-op breakdown, not sequential phases.
• The file:line keys drop the old "Assembly"/etc. labels.

Progress/cancel semantics and the release build are unchanged - timing only records with a ctx attached, under MANIFOLD_DEBUG/_TIMING.

[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.89%. Comparing base (37125da) to head (e458f21).

Files with missing lines	Patch %	Lines
src/execution_impl.cpp	57.14%	6 Missing ⚠️
src/boolean_result.cpp	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1745      +/-   ##
==========================================
- Coverage   94.93%   94.89%   -0.05%     
==========================================
  Files          37       37              
  Lines        8377     8377              
==========================================
- Hits         7953     7949       -4     
- Misses        424      428       +4     

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[elalish]

What will happen if a and b are themselves the result of a tree of boolean operations and everything gets evaluated in parallel at Status? What will the timing prints look like?

[zmerlynn]

Good catch - it was a real bug. The timing baseline lived on the shared ExecutionContext, so parallel Result calls clobbered each other's deltas and the lines interleaved unattributably.

Fixed: the baseline is now a per-Result stack local, and each line carries a per-boolean uid. Still interleaved (eval is parallel), but each boolean's deltas are correct and splittable by tag:

  [b0] phase 7 = 0.026 ms
  [b1] phase 1 = 0.001 ms
  [b0] phase 8 = 0.228 ms   <- since b0's phase 7, not b1's
  [b1] phase 2 = 0.017 ms

grep '\[b0\]' recovers b0's clean 1..11. Static factories (single-threaded) are unchanged. Verified race-free under TSan.