math/nlopt: Update to NLopt 2.9.1

Changes:

NLopt 2.10.0
  - New Java bindings (#578).
  - Allow disabling exceptions with set_exceptions_enabled (#580).
  - Configurable tolg tolerance parameter for Luksan gradient stopping
    condition (#585).
  - Restored LD_LBFGS_NOCEDAL enum value (dropped in 2.9) to ease backwards
    compatibility for wrappers in other languages (though this algorithm is
    currently unimplemented) (#587).

NLopt 2.9.1
  - Fixed PRAXIS box constraints ([#528])

NLopt 2.9.0
  - New NLOPT_LUKSAN cmake option to build without Luksan LGPL code (#568).
  - Dropped unused LD_LBFGS_NOCEDAL enum value.
  - Python 3.13 support (#565).
  - Fixed COBYLA not returning the optimum (#57)
  - Fixed SLSQP returning infeasible optimum (#368)
  - Fixed STOGO not registering new optimum (#504)
  - Various minor bugfixes (#570, #563, #379, #511)

NLopt 2.8.0
  - Support C++ functors for objective functions (#457).
  - CCSA/MMA an now use the initial_step parameter to bound their initial
    stepsize, and also expose a new internal parameter rho_init (#561).
  - Install pkg-config file on Windows (#534).
  - Allow having more equality constraints than there are variables (#509).
  - Bugfixes to nlopt_algorithm_name (#558), Matlab NLOPT_GN_AGS (#533), forced
    stop for empty dimensions (#473), SLSQP (#465), and build improvements
    (#551, #535,#510, #445#).

NLopt 2.7.1
  - Various minor bugfixes (#268, #409, #420) and build
    improvements (support Octave 6.x, Guile 3.x, Cmake 3.2).

NLopt 2.7.0
  - New nlopt_set_param API for setting internal algorithm parameters ([#365]).
  - Avoid library-symbol conflicts ([#355], [#361])

NLopt 2.6.2
  - Fixed forced stop exception with dimension elimination ([#317])
  - Fixed get_initial_step wrapping ([#319])
  - Various build fixes ([#314], [#308], [#303], [#278])

NLopt 2.6.1
  - Fix nlopt_version return value for 2.6.x and update soname and docs.

NLopt 2.6.0
  - New set_upper_bound and set_lower_bound functions in the low-level C API to
    set one bound at a time (#257). There is no longer a separate libnlopt_cxx
    library - C++ algorithms (stogo) are compiled and included by default
    (#198). Various build fixes (#197, #216, #245, #250, #230, #261, etc.),
    other fixes (#242, #258).

NLopt 2.5.0
  - See NEWS: switch to cmake, various new functions, a new algorithm.
