chore: add nix flake configuration for reproducible builds

[MBanucu]

Summary

• Adds flake.nix for Nix flake configuration
• Adds flake.lock for reproducible builds

Summary by CodeRabbit

• Chores
  • Added development environment configuration to streamline setup for contributors with consistent build tools and dependencies.

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[coderabbitai]

Walkthrough

A new Nix flake configuration file has been added to the project. The flake defines development environment inputs (nixpkgs and flake-utils) and configures per-system development shells with build dependencies including cargo, rustc, and bun.

Changes

Cohort / File(s)	Summary
Nix Flake Configuration flake.nix	New file: Defines Nix flake inputs and outputs; creates per-system development shells with cargo, rustc, and bun as build inputs

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A flake so fresh, a config divine,
With shells and inputs, all aligned,
Cargo and rustc, bun in the fold,
Dev environments, a joy to behold! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title accurately describes the main change: adding a Nix flake configuration for reproducible builds. It is concise, specific, and directly related to the changeset.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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