Apply refurb suggestions

[DimitriPapadopoulos]

• [FURB125]: Return is redundant here
• [FURB108]: Use x in (y, z) instead of x == y or x == z
• [FURB124]: Use x == y == z instead of x == y and x == z
• [FURB118]: Replace lambda with operator.mul

[DimitriPapadopoulos]

Reverted changes to xcpy module, see https://github.com/jjhelmus/nmrglue/pull/179#issuecomment-1340210384.

[jjhelmus]

LGTM. Thanks for the modernization.