Change negative Duration format to align with ISO 8601-2:2019

[BastienClement]

Fixes #121

[Copilot]

Pull Request Overview

Updates the Duration format for negative values to align with ISO 8601-2:2019 standard by moving the negative sign to the beginning of the entire duration string rather than applying it to individual components.

• Changes negative duration format from PT-1M-2S to -PT1M2S
• Updates the toISOString() method to handle negative sign placement correctly
• Updates all corresponding test cases to match the new format

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Duration.php	Modifies the toISOString() method to place negative sign at the beginning of the duration string
tests/DurationTest.php	Updates test data provider to match the new negative duration format

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[BenMorel]

Excellent, thank you @BastienClement! And sorry for the review delay.

[BenMorel]

Released as 0.8.0.