Polish lazy_format!

[hildebrandmw]

I recently used this utility and noticed that the docs were a little out of date.

In addition, with some extra work (i.e., adding a move variant to lazy_format!), the created LazyString can be both 'static and Debug, allowing it to be passed to ANNError::message. This enables error reporting like

let x = "context";
let y = 10;

let err = ANNError::message(
    ANNErrorKind::Opaque,
    lazy_format!(move, "error message: {x} - {y}),
);

The generated code is as-if we wrote

let x = "context";
let y = 10;

#[derive(Debug)]
struct Message {
    x: &'static str,
    y: usize,
}

impl std::fmt::Display for Message {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "errro message: {} - {}", self.x, self.y)
    }
}

let err = ANNError::message(
    ANNErrorKind::Opaque,
    Message { x, y }
);

But is more ergonomic to construct. The main benefit here is that it moves string formatting out of the error construction site and up to the error reporting site. Depending on the context, this code motion can clean up the lower level code.

[Copilot]

Pull request overview

This PR updates the documentation for the lazy_format! macro (and related LazyString type) in diskann-utils, aiming to better reflect current behavior and provide clearer, example-driven guidance.

Changes:

• Replaces outdated/async-logging-focused docs with a focused description of lazy_format! and how it defers formatting.
• Adds a richer rustdoc example demonstrating deferred formatting behavior.
• Cleans up the LazyString implementation to use std::fmt::Result directly.

---

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Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.50%. Comparing base (6caca35) to head (451d2df).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1274   +/-   ##
=======================================
  Coverage   91.50%   91.50%           
=======================================
  Files         498      498           
  Lines       95522    95536   +14     
=======================================
+ Hits        87407    87424   +17     
+ Misses       8115     8112    -3     

Flag	Coverage Δ
miri	91.50% <100.00%> (+<0.01%)	⬆️
unittests	91.47% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann-utils/src/lazystring.rs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[Copilot]

Pull request overview

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Comments suppressed due to low confidence (1)

diskann-utils/src/lazystring.rs:84

• Same hygiene issue as the move arm: the non-move arm uses an unqualified write!, which can be shadowed by downstream macros at the expansion site. Use a fully qualified macro path such as ::core::write!.

            write!(f, $($arg)*)

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Comments suppressed due to low confidence (1)

diskann-utils/src/lazystring.rs:63

• The docs imply that using lazy_format!(move, ...) produces a 'static LazyString, but move only captures arguments by value; the result is 'static only if the captured values themselves are 'static (or owned types that don’t borrow). Clarifying this avoids misleading users into thinking move guarantees 'static.

/// The default [`LazyString`] created by this macro borrows from its formatted arguments
/// and thus has a lifetime constrained to its arguments.
///
/// If a lazily formatted `'static` compliant variation is needed, the "move" variant
/// can be used:
///

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Pull request overview

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