chore: Add script to show the sizes of futures (async Rust)

[Hocuri]

Add the script from https://github.com/chatmail/core/pull/8345/changes#r3696015000 with a few small tweaks

[link2xt]

I pinned one of the largest futures, this helps: #8537

There is however still a pgp message decryptor that is huge (tens of kbtes), is returned from decrypt and increases the size of all imap fetch functions:

print-type-size type: `pgp::composed::Message<'_>`: 4544 bytes, alignment: 16 bytes
print-type-size     variant `Encrypted`: 4537 bytes
print-type-size         field `.edata`: 4512 bytes
print-type-size         field `.esk`: 24 bytes
print-type-size         field `.is_nested`: 1 bytes
print-type-size     variant `Compressed`: 217 bytes
print-type-size         padding: 16 bytes
print-type-size         field `.reader`: 200 bytes, alignment: 8 bytes
print-type-size         field `.is_nested`: 1 bytes
print-type-size     variant `Literal`: 193 bytes
print-type-size         padding: 16 bytes
print-type-size         field `.reader`: 176 bytes, alignment: 8 bytes
print-type-size         field `.is_nested`: 1 bytes
print-type-size     variant `Signed`: 105 bytes
print-type-size         padding: 16 bytes
print-type-size         field `.reader`: 88 bytes, alignment: 8 bytes
print-type-size         field `.is_nested`: 1 bytes
print-type-size     end padding: 7 bytes

This should be boxed, maybe even inside of pgp. pgp has #[allow(clippy::large_enum_variant)] in multiple places, and this is why it is a problem, these variants should be boxed. We can box the whole message as a workaround.

[link2xt]

The lint is currently disabled, we can reenable it back if the problem is fixed: #8487

[link2xt]

For reference: https://nnethercote.github.io/perf-book/type-sizes.html
If we shrink down receive_imf size, can also add a test to make sure its size is below some reasonable size.