track_caller for capacity overflow panics

[kornelski]

'CapacityError: insufficient capacity' panic points to ~/.cargo/registry/src/github.com-1ecc6299db9ec823/arrayvec-0.7.2/src/arrayvec.rs:176:9 instead of the line of user code that pushed.

#[track_caller] makes this error more relevant to users.

[bluss]

Thanks, it does make sense. track_caller is supposed to have some overhead, but I can't find it quantified anywhere. I suppose it's not API-defining anyway, so worst case it can always be changed around - just saying that to make it easy for us to include this change.

[kornelski]

It has overhead of having an extra function argument, but when used with small generic functions, the calls and their arguments get inlined, so the overhead usually disappears.