docs: Add NumPy ndarray.flat term entry (#7874)

[Rishabh1925]

Closes #7874

This Pull Request adds the documentation entry for the fundamental NumPy ndarray attribute, .flat.

Implementation Details:

• File Path: Created the file at the required location: docs/content/numpy/concepts/ndarray/terms/flat/flat.md.
• Core Concept: The entry defines .flat as a 1-D iterator, demonstrating how to access elements linearly in multi-dimensional arrays without needing nested loops.
• Functionality: The examples illustrate both iteration and direct assignment using the iterator.
• Structure: Includes the mandatory Description, Syntax, Example, and Codebyte sections.

[Rishabh1925]

Hello @mamtawardhani @codecademy-docs
I have finished creating the new term entry for ndarray.flat.
The documentation clearly explains the concept of 1-D iteration and includes a runnable Codebyte. Ready for review!

[mamtawardhani]

Looks good for a second review! 🚀

[Rishabh1925]

Hey @mamtawardhani please look into pr and merge this please, after which i can work on more issues,

Thanks a lot

[Rishabh1925]

@mamtawardhani @dakshdeepHERE Please look into this PR.....and merge this please

[Sriparno08]

Looks good, @Rishabh1925!

[github-actions]

👋 @Rishabh1925
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