opts.spread_kerevalmeth should be uint16_t throughout

[ahbarnett]

kerevalmeth should be chnaged to uint16_t throughout (eg in templating, no true/false), as it is mixed up currently... we may introduce methods >1 in future... Thanks! Alex

[DiamonDinoia]

we are working on simplifying the dispatch to increase clarity and allow more parameters to fit into kernels: https://godbolt.org/z/GM94xb1j4

Once this is ready the code will be refactored.

[ahbarnett]

Mentioned in mtg of 8/20/24 as a needed clean-up of templating. (some are uint16_t, as needed, others bool). Thanks @DiamonDinoia