Add NICO Game Framework to Tiled support documentation

[Copilot]

Adds the NICO Game Framework to the "Support by Framework" section of the Tiled documentation page.

Overview

NICO is a game framework for the Nim programming language that supports loading and saving Tiled maps in JSON format through its loadMap and saveMap functions.

Changes

• Added NICO Game Framework entry under "Support by Framework" section in docs/reference/support-for-tmx-maps.rst
• Positioned alphabetically between "Monkey X" and "Node.js" sections
• Included link to the Tilemap API documentation for reference

Documentation Screenshot

The documentation now includes NICO, providing support coverage for the Nim programming language ecosystem.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Tiled support for Nim language</issue_title>
<issue_description>Nim language has library called Nico that supports Tiled's JSONs according to its description. Could be good to be included in here so the language is also covered ^^</issue_description>

<agent_instructions>Please add NICO Game Framework to the linked documentation page under "Support by Framework", also including a link to the relevant documentation.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@bjorn It is documented at https://github.com/ftsf/nico/blob/main/API.md#tilemap, which says there are `loadMap` and `saveMap` functions that use Tiled's JSON format.

The project does not appear very actively developed, but it does seem worth adding.</comment_new>

Fixes #4255

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