Replace the LangChain version of Mustache to chevron

[YusakuNo1]

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[Copilot]

PR Overview

This PR replaces the LangChain version of Mustache with the chevron library in the Prompty system to update the template rendering implementation.

• Updated pyproject.toml to add chevron and its type definitions.
• Modified renderers.py to import render from chevron instead of the previous mustache module.

Reviewed Changes

File	Description
runtime/prompty/pyproject.toml	Added chevron and types-chevron dependencies to align with the upgrade.
runtime/prompty/prompty/renderers.py	Replaced the mustache import with chevron's render function for template rendering.

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.