Add needless_type_cast lint

[borngraced]

Clippy should warn when a const, static, or let binding is defined as one integer type but immediately/ consistently cast to another type at usage sites without any usage of the original type. fixes #16137

changelog: [needless_type_cast ]: suggests defining bindings as their cast type

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[github-actions]

Lintcheck changes for 48f7f36

Lint	Added	Removed	Changed
clippy::needless_type_cast	8	0	0

This comment will be updated if you push new changes

[ada4a]

Looking at Lintcheck, at least the prost warnings seem to be FPs, let len: usize = iter.sum(); len as u64 is necessary, as iter is an Iterator<Item=usize>, and so can't be .sum()-ed up to a u64.

Judging by the comment in rustix, the warning seems to be a FP as well, because let fd: libc::c_int = fd; is effectively a cast, though I'm not fully sure about this one.

I don't really know how one would go on about recognizing such FPs, so maybe this lint would just need to be pedantic