2.0 Remove `copy(x)` for immutables

[jariji]

#45143 and #31995 (comment) prefer not to define copy for immutables. Currently copy is defined for a bunch of types like <: Number that don't need it, which could be removed.

[jakobnissen]

Cross-ref:

• add a fallback copy method for isbits values #53938
• 2.0 Remove copy(x) for immutables #53970
• Define copy for immutable values #45143
• copy not implemented for String #31995 (comment)