Delete #[automatically_derived] on impl blocks that are not trait impls

[dtolnay]

Rustc nightly-2025-07-19 has begun warning about this. rust-lang/rust#143845

warning: `#[automatically_derived]` only has an effect on trait implementation blocks
  --> demo/src/main.rs:23:12
   |
23 |         fn put(&self, parts: &mut MultiBuf) -> u64;
   |            ^^^
   |
   = note: `#[warn(unused_attributes)]` on by default

warning: `#[automatically_derived]` only has an effect on trait implementation blocks
  --> demo/src/main.rs:24:12
   |
24 |         fn tag(&self, blobid: u64, tag: &str);
   |            ^^^

warning: `#[automatically_derived]` only has an effect on trait implementation blocks
  --> demo/src/main.rs:25:12
   |
25 |         fn metadata(&self, blobid: u64) -> BlobMetadata;
   |            ^^^^^^^^