docs: improve doctests for complex number instances in `strided/base/cmap`

[prajjwalbajpai]

Resolves a part of #8641.

Description

This pull request:

• Updates REPL and documentation examples in the strided/base/cmap package to use the compact complex instance doctest notation.
• Replaces example decomposition using realf/imagf with concise doctest annotations.

Related Issues

This pull request has the following related issues:

• #8641

Questions

No.

Other

No.

Checklist

• [x] Read, understood, and followed the contributing guidelines.

AI Assistance

• [ ] Yes
• [x] No

If you answered "yes" above, how did you use AI assistance?

• [ ] Code generation (e.g., when writing an implementation or fixing a bug)
• [ ] Test/benchmark generation
• [ ] Documentation (including examples)
• [ ] Research and understanding

Disclosure

NA

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Coverage Report

Package	Statements	Branches	Functions	Lines
strided/base/cmap	$\color{green}226/226$ $\color{green}+100.00%$	$\color{green}9/9$ $\color{green}+100.00%$	$\color{green}2/2$ $\color{green}+100.00%$	$\color{green}226/226$ $\color{green}+100.00%$

The above coverage report was generated for the changes in this PR.