Review and clean up ChatGPT-generated Nelder-Mead implementation

Fix bugs: error message typo ("Min not be" -> "Min must not be"),
validation messages using wrong bracket notation ([0,1] -> (0,1) for
exclusive bounds), swapped format args in expectPoint test helper,
mislabeled NaN-Min test case, and missing empty-x0 validation.

Clean up code: replace setZero with clear builtin, rename misleading
reflect method to transformPoint, remove unnecessary buffer zeroing
in replacePoint, remove redundant n parameter from createSimplex,
simplify createSimplex with copy, use min/max builtins in constraint
clamping, and add comments to algorithm steps throughout.

Trim verbose ChatGPT-style doc comments to concise idiomatic Go.

Author: crhntr