Fix some bug risks and code quality issues

[sanketsaurav]

Changes:

• Remove redundant import alias name in prompt_toolkit/contrib/telnet/server.py
• Use enumerate() to cycle through an iterable with counting in prompt_toolkit/widgets/base.py and prompt_toolkit/layout/processors.py
• Use in to check if a value is equal to two or more other values in prompt_toolkit/key_binding/key_bindings.py
 - Removed unnecessary list comprehension in prompt_toolkit/output/win32.py

Also added a .deepsource.toml configuration file to run continuous static analysis on the repository with DeepSource.

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This PR also adds .deepsource.toml configuration file to run static analysis continuously on the repo with DeepSource. Upon enabling DeepSource, quality and security analysis will be run on every PR to detect 500+ types of problems in the changes — including bug risks, anti-patterns, security vulnerabilities, etc.

DeepSource is a free to use for open-source projects, and is used by teams at NASA, Uber, Slack among many others, and open-source projects like ThoughtWorks/Gauge, Masonite Framework, etc.

To enable DeepSource analysis after merging this PR, please follow these steps:

1. Sign up on DeepSource with your GitHub account and grant access to this repo.
2. Activate analysis on this repo here.

You can also look at the docs for more details. Do let me know if I can be of any help!

Cheers,

Sanket
Founder, DeepSource

[hartwork]

• Use enumerate() to cycle through an iterable with counting in prompt_toolkit/widgets/base.py and prompt_toolkit/layout/processors.py

• Use in to check if a value is equal to two or more other values in prompt_toolkit/key_binding/key_bindings.py
 - Removed unnecessary list comprehension in prompt_toolkit/output/win32.py

Out of curiosity, is this about readability or performance or …? The reasoning behind those changes does not seem obvious. Thanks!