fix(rustify_derive): remove derive block expr to fix LSP type inference

[lazulit3]

This updates rustify_derive to remove the block expression that the impl Endpoint was wrapped in.

This resolves an issue where rust-analyzer is unable to infer the type of Endpoint::Response in some cases. The issue is described at:

• rust-analyzer fails to infer types for Endpoint::Response #28

🔧 Changes

• Removes the block expression const #const_ident: () = {...}; wrapping impl Endpoint in the derive macro
• Removes the convenience use imports that were contained in this block expression
• Updates usage of those imported types to use fully qualified type paths e.g. RequestMethod -> rustify::enums::RequestMethod

◀️ Backwards-Compatibility

I believe this fix is backwards-compatible, but I invite others to check me on that.

Since vaultrs uses rustify, I checked vaultrs on master (aaa7ff6) with rustify_derive dependency pointed at this branch.

cargo build succeeds and cargo clippy reports two unused serde::Serialize imports:

warning: unused import: `serde::Serialize`
 --> src/api/identity/entity_alias/requests.rs:5:5
  |
5 | use serde::Serialize;
  |     ^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused import: `serde::Serialize`
 --> src/api/identity/entity/requests.rs:2:5
  |
2 | use serde::Serialize;
  |     ^^^^^^^^^^^^^^^^

This is likely due to switching to serde::Serialize in the macro. I think not requiring this use is an improvement, but if we prefer I can adjust the PR.

✅ Testing

• Verified that these changes allow rust-analyzer to infer response types in my editor.
  • I tested this with the same example case described in rust-analyzer fails to infer types for Endpoint::Response #28, as well as in my project using this library.
• Ran checks/lints/tests/examples locally:
  • cargo test
  • cargo check
  • cargo clippy
  • cargo run --package rustify --example reqres1
  • cargo run --package rustify --example reqres2