use 'convert' as more precise term than 'cast' for the conversion from sstr_t to scstr_t

unifies naming of sstr_t related and scstr_t related functions

adds remaining documentation for the scstr functions

overflow of sstrnlen should return SIZE_MAX instead of zero

adjusts documentation of UCX string types, converters, and constructors

finally removes the underscore of ugliness from ucx_str_cmp() and ucx_str_casecmp()

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mercurial