Fix: auto-cast to correct type when using vconstant

[JovanVeljanoski]

See discussion at https://github.com/vaexio/vaex/issues/2286 This is largely inspired by the proposal of @NickCrews in https://github.com/vaexio/vaex/issues/2286

Checklist:

• [x] Create unit test
• [x] Unit-test passes
• [ ] Review

[NickCrews]

Looks like the right idea to me, but looks like it fails the unit tests when you give it a values of [1, 2]

[JovanVeljanoski]

Yeah I overlooked that case, i will handle it in the next iteration :). Thanks!

[JovanVeljanoski]

It should be fine now.. i've extended your idea @NickCrews to also be applied to lists.. if that is ever is needed. For example:

import vaex

length = 3
df = vaex.from_arrays(x=[1, 2, 3])
df['list_floats'] = vaex.vconstant(value=[1, 2, 3], length=length, dtype='float')
df['list_ints'] = vaex.vconstant(value=[1, 2, 3], length=length, dtype='int')
df['list_strings'] = vaex.vconstant(value=[1, 2, 3], length=length, dtype='str')

would do the equivalent thing, but now within the lists!