Refactor `iszero()` and `isnan()` to accept all numeric types

[Jefffrey]

Is your feature request related to a problem or challenge?

Currently iszero() and isnan() coerce inputs to float to compute:

datafusion/datafusion/functions/src/math/iszero.rs

Lines 61 to 71 in a02e683

	pub fn new() -> Self {
	// Accept any numeric type and coerce to float
	let float = Coercion::new_implicit(
	TypeSignatureClass::Float,
	vec![TypeSignatureClass::Numeric],
	NativeType::Float64,
	);
	Self {
	signature: Signature::coercible(vec![float], Volatility::Immutable),
	}
	}

datafusion/datafusion/functions/src/math/nans.rs

Lines 57 to 67 in a02e683

	pub fn new() -> Self {
	// Accept any numeric type and coerce to float
	let float = Coercion::new_implicit(
	TypeSignatureClass::Float,
	vec![TypeSignatureClass::Numeric],
	NativeType::Float64,
	);
	Self {
	signature: Signature::coercible(vec![float], Volatility::Immutable),
	}
	}

Describe the solution you'd like

Consider refactoring these to accept numeric types without coercing to float; the implementations should be simple (albeit verbose/tedious). For example, isnan() should return false for any numeric inputs that aren't float type, which might be a slight optimization.

Describe alternatives you've considered

If we prefer to keep the code simple we can leave it as is

Additional context

No response