Inconsistent comment handling in tuple field formatting

Given code like this:

struct S {
    field1: (/* */),
    field2: (/* */u32/* */),
    field3: (/* */u32,/* */),
}

rustfmt 1.8.0-stable formats it as:

struct S {
    field1: (),
    field2: (u32),
    field3: (/* */ u32 /* */,),
}

Shouldn't the formatted result be one of the following instead?

struct S {
    field1: (/* */),
    field2: (/* */ u32 /* */),
    field3: (/* */ u32 /* */,),
}

or

struct S {
    field1: (),
    field2: (u32),
    field3: (u32,),
}

Reproduce the reported output from issue #6642 with the tuple-field snippet using rustfmt 1.8.0-stable. Determine whether tuple comments should be preserved or removed consistently, then add regression coverage showing the chosen formatting for all three fields.