Fix clippy warning about unnecessary Default

[mhansen]

Fixes #120

error: this `impl` can be derived
  --> src/unzip/seekable_http_reader.rs:54:1
   |
54 | / impl Default for AccessPattern {
55 | |     fn default() -> Self {
56 | |         Self::RandomAccess
57 | |     }
58 | | }
   | |_^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.91.0/index.html#derivable_impls
   = note: `-D clippy::derivable-impls` implied by `-D clippy::all`
   = help: to override `-D clippy::all` add `#[allow(clippy::derivable_impls)]`
help: replace the manual implementation with a derive attribute and mark the default variant
   |
45 + #[derive(Default)]
46 ~ pub(crate) enum AccessPattern {
47 |     /// We expect accesses all over the file.
48 ~     #[default]
49 ~     RandomAccess,
   |