FlahaX competitor comparison (#40)

Measured commit: ed568c5a7affaf0d17ee72798c7a708af6cec7c6
Python 3.13.15 on Windows-11-10.0.26200-SP0

formulation.json  FlahaX vs Horticalc v0.6.7 vs an Irriblend-method LP baseline
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: benchmarks/competitors/README.md in the repository at the measured commit.
Timings are best of three on one machine; compare them only within this snapshot.
