Consider year based temporal encoding

[meiertgrootes]

For training to be able to capture yearly cycles the temporal encoding should reflect this. -> try cyclic embedding on a full duration

Linken question: Are we going to work with a calendar year or go for the "360 day year" Chris mentioned

Sin and cos functions over this period

[SarahAlidoost]

@meiertgrootes now there is a documentation on encoder_decoder, see https://github.com/ESMValGroup/ClimaNet/blob/main/docs/code_math_description.md. Also, you might consider creating a branch based on #24.