Replace lazy_static with std::sync::LazyLock

[gcomte]

Summary

• Replace lazy_static! macro with std::sync::LazyLock (stable since Rust 1.80)
• Remove lazy_static crate dependency

Test plan

• cargo check passes
• CI build + tests pass

Summary by CodeRabbit

• Refactor
  • Removed an external dependency and modernized the lazy initialization mechanism by switching to a built-in standard library alternative. This reduces external dependencies, improves code maintainability, and ensures all existing functionality remains intact with no user-facing impact.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 16140f98-1773-4e15-b1a7-39625f8beb24

📥 Commits

Reviewing files that changed from the base of the PR and between 6fdec08 and 900ce58.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• Cargo.toml
• src/currency/fiat.rs

💤 Files with no reviewable changes (1)

• Cargo.toml

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📝 Walkthrough

Walkthrough

This pull request migrates the EXCHANGE_RATE_PROVIDER static initialization from the external lazy_static crate to Rust's built-in std::sync::LazyLock, eliminating the external dependency while preserving identical functionality.

Changes

Cohort / File(s)	Summary
Dependency Removal Cargo.toml	Removed lazy_static = "1.5.0" from dependencies.
LazyLock Migration src/currency/fiat.rs	Replaced lazy_static! macro with std::sync::LazyLock for EXCHANGE_RATE_PROVIDER initialization; updated imports to remove lazy_static::lazy_static and add std::sync::LazyLock. Locking behavior in Fiat::btc_value() remains unchanged.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• Refactor exchange rate caching #370: Modifies the same EXCHANGE_RATE_PROVIDER initialization in src/currency/fiat.rs, replacing an earlier unsafe static pattern with lazy_static! and Mutex, making this PR a direct successor migration to Rust's built-in LazyLock.

Poem

Lazy static fades away,
LazyLock leads the way! 🐰
Built-in magic, swift and true,
Dependencies, one fewer hue,
Rust's own power sees us through! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Replace lazy_static with std::sync::LazyLock' accurately describes the primary change: migrating from the lazy_static crate to Rust's built-in LazyLock mechanism, including removing the external dependency.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/replace-lazy-static

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