- Add sampler/common.rs with distribution helpers (internal_bounds,
from_internal, to_internal, sample_random) used by 8 samplers
- Add sampler/tpe/common.rs with TPE sampling functions
(sample_tpe_float, sample_tpe_int, sample_tpe_categorical)
shared by TpeSampler, MultivariateTpeSampler, and MotpeSampler
- Remove ~940 lines of near-identical code across sampler modules