[ENH] Added Informer Network to aeon/networks

[lucifer4073]

Reference Issues/PRs

Fixes #2921.

What does this implement/fix? Explain your changes.

Implements Informer network based on the standard implementation.

https://github.com/lucifer4073/Informer2020/tree/main/models

Does your contribution introduce a new dependency? If yes, which one?

Any other comments?

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I have added the following labels to this PR based on the title: [ enhancement ].
I have added the following labels to this PR based on the changes made: [ networks ]. Feel free to change these if they do not properly represent the PR.

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[lucifer4073]

Hi @hadifawaz1999,

A few points regarding the implementation:

1. Since Informer does not follow a strict auto-encoder or encoder structure and primarily uses attention mechanisms, I’ve placed it under the transformer module.
2. ProbAttention could be useful for future implementations, so I’ve added it to utils/networks to keep it reusable and modular. Including it directly within the Informer implementation would have made the code unnecessarily cluttered. Open to any suggestions on this.