fix arithmetic side effects false positive

[pocopepe]

fixes #17005

changelog: [arithmetic_side_effects]: don't lint when one operand is an as cast from a smaller integer type

[rustbot]

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[github-actions]

Lintcheck changes for a5244cc

Lint	Added	Removed	Changed
clippy::arithmetic_side_effects	0	39	3

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[Jarcho]

Thank you.

View changes since this review

[simonsso]

@pocopepe does it handle the corner case when adding 0xffff_0001 + id_u16() which still could wrap ?

[pocopepe]

yes it does, considering the check computes const + u16::MAX and only suppresses if the result fits in u32, so 0xffff_0001 + 65535 still warns as expected :)