centralize b-value management at initialization (#155)

[Devguru-codes]

• Remove bvalues parameter from all 27 algorithm ivim_fit() and ivim_fit_full_volume() signatures in src/standardized/
• All algorithms now access b-values via self.bvalues exclusively
• Add **kwargs to algorithms that lacked it (OJ_GU_seg, PV_MUMC, PvH_KB_NKI, TF_reference)
• OsipiBase.osipi_fit() and osipi_fit_full_volume() enforce ValueError if bvalues not set at init
• Update all test files to pass bvalues at OsipiBase(...) init
• Update WrapImage production wrappers to use new API
• Remove now-redundant bvalue equality checks in DL algorithms

fixes #155