fix: format 8 digits chilean rut

[dagalloso]

The current implementation of the format method does not support 8-digit RUTs (Chile), resulting in an unexpected undefined at the end. This type of RUT is common among people over 60 years old.

Current response: "77.272.305-undefined"
Expected: "7.727.230-5"

[gemini-code-assist]

Summary of Changes

Hello @dagalloso, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical formatting bug in the Chilean RUT utility. Previously, the format method failed to correctly process 8-digit RUTs, which are common for individuals over 60, resulting in malformed output. The core change involves updating the formatting logic to use precise string slicing, ensuring all valid RUT lengths are handled correctly. This enhancement improves the reliability and accuracy of the RUT formatting functionality.

Highlights

• Bug Fix: Resolved an issue where the format method for Chilean RUTs incorrectly handled 8-digit numbers, leading to an 'undefined' segment in the formatted output.
• Improved Formatting Logic: The format method in src/cl/rut.ts has been refactored to use string slicing, providing a more robust and accurate way to format RUTs of varying lengths.
• Test Coverage: A new test case has been added to src/cl/rut.spec.ts specifically to validate the correct formatting of 8-digit RUTs, ensuring the fix works as expected.

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[gemini-code-assist]

Code Review

This pull request successfully addresses an issue with formatting 8-digit Chilean RUTs. The previous implementation failed on shorter RUTs, and the new logic using slice with negative offsets correctly handles both 8 and 9-digit RUTs. A new test case has been added to cover this scenario, which is great. I've provided one suggestion to improve the readability and maintainability of the formatting logic using a regular expression.

[gemini-code-assist]

While the use of multiple slice() calls is correct, it can be a bit difficult to read and verify the indices at a glance. A regular expression can make this formatting logic more declarative and easier to understand. It also has the benefit of not producing a malformed string if the input doesn't match the expected RUT structure (e.g., for inputs with an incorrect length).

Suggested change

	return `${value.slice(0, -7)}.${value.slice(-7, -4)}.${value.slice(-4, -1)}-${value.slice(-1)}`;
	return value.replace(/^(\d{1,2})(\d{3})(\d{3})(.)$/, '$1.$2.$3-$4');