FlahaX competitor comparison (#40)

Measured commit: 1ade5b666f5381b5fedcba2c1fce84fea784f261
Python 3.13.15 on Windows-11-10.0.26200-SP0

formulation.json  FlahaX vs Horticalc v0.6.7 vs Irriblend-DSW (a046d5c) and an LP after its method
chemistry.json    FlahaX vs live PHREEQC (PhreeqPython 1.6.2) on the golden fixtures
ec.json           EC25 against IUPAC KCl primary standards, and catalogue agreement
environment.json  interpreter, platform and the full package list of the run

Protocol: tools/competitors/README.md in the repository at the measured commit
(benchmarks/competitors/README.md before #64).
Timings are best of three on one machine; compare them only within this snapshot.
