fix: remove doc_auto_cfg and doc_cfg_hide

[loyd]

These attributes were removed:

error[E0557]: feature has been removed
 --> /home/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cordyceps-0.3.4/src/lib.rs:2:38
  |
2 | #![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg, doc_cfg_hide))]
  |                                      ^^^^^^^^^^^^ feature has been removed
  |
  = note: removed in 1.92.0; see <https://github.com/rust-lang/rust/pull/138907> for more information
  = note: merged into `doc_cfg`

error[E0557]: feature has been removed
 --> /home/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cordyceps-0.3.4/src/lib.rs:2:52
  |
2 | #![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg, doc_cfg_hide))]
  |                                                    ^^^^^^^^^^^^ feature has been removed
  |
  = note: removed in 1.92.0; see <https://github.com/rust-lang/rust/pull/138907> for more information
  = note: merged into `doc_cfg`

So, it's impossible to build documentation for downstream crates.

[loyd]

It seems the version specified in rust-toolchain.toml (2025-07-20) still requires doc_cfg_hide. Some options here:

1. Update the toolchain
2. Remove these attributes only for crates that don't require doc_cfg_hide (like cordyceps)
3. Add doc_cfg_hide based on the version

@hawkw WDYT?