add num-complex requirement

[mwlon]

Which issue does this PR close?

Closes #3849

Rationale for this change

More correct package dependencies.

arrow-array relies on the num-complex crate and uses its ComplexFloat trait, but that was only released in 0.4.2. The num dependency alone only requires num-complex 0.4.0, so this can cause compilation errors:

error[E0432]: unresolved import `num::complex::ComplexFloat`
  --> /Users/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-30.0.1/src/arithmetic.rs:21:5
   |
21 | use num::complex::ComplexFloat;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ no `ComplexFloat` in `complex`

error[E0599]: no method named `powi` found for struct `f16` in the current scope
   --> /Users/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-30.0.1/src/arithmetic.rs:351:25
    |
351 |                 Ok(self.powi(exp as i32))
    |                         ^^^^ method not found in `f16`
...
380 | native_type_float_op!(f16, f16::ONE, f16::ZERO);
    | ----------------------------------------------- in this macro invocation
    |
    = help: items from traits can only be used if the trait is in scope
    = note: this error originates in the macro `native_type_float_op` (in Nightly builds, run with -Z macro-backtrace for more info)
help: the following traits are implemented but not in scope; perhaps add a `use` for one of them:
    |
18  + use num::Float;
    |
18  + use num::traits::float::FloatCore;
    |
18  + use num::traits::real::Real;
    |

error[E0599]: no method named `powi` found for struct `f16` in the current scope
   --> /Users/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-30.0.1/src/arithmetic.rs:356:22
    |
356 |                 self.powi(exp as i32)
    |                      ^^^^ method not found in `f16`
...
380 | native_type_float_op!(f16, f16::ONE, f16::ZERO);
    | ----------------------------------------------- in this macro invocation
    |
    = help: items from traits can only be used if the trait is in scope
    = note: this error originates in the macro `native_type_float_op` (in Nightly builds, run with -Z macro-backtrace for more info)
help: the following traits are implemented but not in scope; perhaps add a `use` for one of them:
    |
18  + use num::Float;
    |
18  + use num::traits::float::FloatCore;
    |
18  + use num::traits::real::Real;
    |

What changes are included in this PR?

Cargo.toml change to arrow-array

Are there any user-facing changes?

no

[tustvold]

Could we perhaps just update the num requirement to 0.4.2?

[mwlon]

@tustvold there is no num 0.4.2. There is only 0.4.0, which depends on num-complex 0.4.0. I think we need to specify the version num-complex specifically.

Filed rust-num/num#426 because this is indeed a bit annoying.