Enable clippy::use_self at workspace level and align codec implementations (#79)

This change enables `clippy::use_self` in workspace lint configuration
so the rule is enforced consistently. It also updates existing Rust
codec code to conform to the newly enabled lint without changing
behavior.

- **Workspace lint configuration**
  - Added `use_self = "warn"` under `[lints.clippy]` in:
    - root `Cargo.toml`
- `fuzz/Cargo.toml` (to keep fuzz crate lint settings aligned with
workspace expectations)

- **Code updates required by `use_self`**
- Replaced explicit type repetitions with `Self` in constructors/default
impls and associated method calls:
    - `src/rust/integer_compression/fastpfor.rs`
    - `src/rust/integer_compression/just_copy.rs`
    - `src/rust/integer_compression/variable_byte.rs`

- **Representative change**
  ```rust
  impl VariableByte {
      #[must_use]
      pub fn new() -> Self {
          Self
      }
  }

  impl Default for VariableByte {
      fn default() -> Self {
          Self::new()
      }
  }
  ```

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: CommanderStorm <26258709+CommanderStorm@users.noreply.github.com>
Co-authored-by: Yuri Astrakhan <yuriastrakhan@gmail.com>

Author: 3 people

Cargo.toml

@@ -53,6 +53,7 @@ missing_docs = "warn"
 [lints.clippy]
 cargo = { level = "warn", priority = -1 }
 pedantic = { level = "warn", priority = -1 }
+use_self = "warn"
 cast_possible_truncation = "allow"
 cast_possible_wrap = "allow"
 cast_sign_loss = "allow"

fuzz/Cargo.toml

@@ -22,6 +22,7 @@ unused_qualifications = "warn"
 [lints.clippy]
 cargo = { level = "warn", priority = -1 }
 pedantic = { level = "warn", priority = -1 }
+use_self = "warn"
 # Allow certain lints that are common in fuzz targets and not worth fixing.
 doc_markdown = "allow"
 wildcard_imports = "allow"

src/rust/integer_compression/fastpfor.rs

@@ -93,7 +93,7 @@ impl<const N: usize> FastPFor<N> {
                 block_size: N as u32,
             });
         }
-        Ok(FastPFor {
+        Ok(Self {
             bytes_container: BytesMut::with_capacity(
                 (3 * page_size / N as u32 + page_size) as usize,
             ),

src/rust/integer_compression/just_copy.rs

@@ -5,20 +5,14 @@ use crate::helpers::AsUsize;
 /// A no-op codec that copies data without compression.
 ///
 /// Useful as a baseline for benchmarking or when a codec interface is required.
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct JustCopy;
 
 impl JustCopy {
     /// Creates a new instance
     #[must_use]
     pub fn new() -> Self {
-        JustCopy
-    }
-}
-
-impl Default for JustCopy {
-    fn default() -> Self {
-        JustCopy::new()
+        Self
     }
 }
 

src/rust/integer_compression/variable_byte.rs

@@ -8,7 +8,7 @@ use crate::rust::cursor::IncrementCursor;
 use crate::{FastPForError, FastPForResult};
 
 /// Variable-byte encoding codec for integer compression.
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct VariableByte;
 
 // Helper functions with const generics for extracting 7-bit chunks
@@ -28,8 +28,8 @@ impl VariableByte {
 impl VariableByte {
     /// Creates a new instance
     #[must_use]
-    pub fn new() -> VariableByte {
-        VariableByte
+    pub fn new() -> Self {
+        Self
     }
 
     /// Compress `input_length` u32 values from `input[input_offset..]` into
@@ -301,20 +301,14 @@ impl VariableByte {
     }
 }
 
-impl Default for VariableByte {
-    fn default() -> Self {
-        VariableByte::new()
-    }
-}
-
 impl AnyLenCodec for VariableByte {
     fn encode(&mut self, input: &[u32], out: &mut Vec<u32>) -> FastPForResult<()> {
         let capacity = input.len() * 2 + 4;
         let start = out.len();
         out.resize(start + capacity, 0);
         let mut in_off = Cursor::new(0u32);
         let mut out_off = Cursor::new(0u32);
-        VariableByte::compress_into_slice(
+        Self::compress_into_slice(
             input,
             input.len() as u32,
             &mut in_off,
@@ -342,7 +336,7 @@ impl AnyLenCodec for VariableByte {
         out.resize(start + capacity, 0);
         let mut in_off = Cursor::new(0u32);
         let mut out_off = Cursor::new(0u32);
-        VariableByte::decompress_from_u32_slice(
+        Self::decompress_from_u32_slice(
             input,
             input.len() as u32,
             &mut in_off,