Adopt libneo species and collision_freqs instead of own implementations

[krystophny]

Context

The libneo dependency audit (itpplasma/libneo#258) identified that QL-Balance in KAMEL currently links LIBNEO::species, LIBNEO::collision_freqs, and LIBNEO::transport, but KAMEL also has its own vendored copies of related code (e.g., plag_coeff.f90 in multiple locations, diverged hdf5_tools).

The team decided that downstream codes should adopt the shared, tested implementations from libneo rather than maintaining their own copies.

Action

1. Verify that QL-Balance uses the libneo species/collision_freqs/transport chain consistently
2. Remove any duplicate or diverged implementations of collision frequency and species calculations within KAMEL
3. Update vendored copies of plag_coeff.f90 and binsrc.f90 to use libneo's modernized versions via FetchContent
4. Replace the vendored KAMEL_hdf5_tools with libneo's hdf5_tools (may require adding missing features to libneo if KAMEL has additions like h5_add_float_1 or h5_append_double_1)

Ref: itpplasma/libneo#258, itpplasma/libneo#266