Update dev env elixir to v1.18

[zoedsoupe]

Problem

The project currently uses an outdated version of Elixir, which may lack recent features and improvements introduced in newer releases. Upgrading to a more recent version can enhance performance, security, and maintainability.

Solution

This pull request updates the project's Elixir version to 1.18. This version introduces several enhancements, including:

• Type System Improvements: Elixir 1.18 introduces type checking of function calls and gradual inference of patterns and return types, enhancing code reliability.

• Language Server Enhancements: The new compiler lock and listener features improve development tooling by allowing multiple Elixir instances to share compilation results, reducing duplicate efforts.

• Built-in JSON Support: A new JSON module provides functions to encode and decode JSON, streamlining data handling without external dependencies.

• ExUnit Enhancements: Support for parameterized tests allows running the same test module multiple times under different parameters, improving test coverage and flexibility.

Rationale

Upgrading to Elixir 1.18 ensures the project benefits from the latest language features and performance improvements. The enhancements in type checking, development tooling, and testing capabilities contribute to a more robust and efficient codebase. Additionally, built-in JSON support reduces reliance on external libraries, simplifying maintenance.

For a comprehensive overview of the new features in Elixir 1.18, you might find the following video informative: