feat(cli): Add shell command

[provinzkraut]

What

Add a shell command to drop into an interactive console. The console namespace is preloaded with the app, and can be customised by plugins. For example, advanced-alchemy could provide its config or a SQLAlchemy session by implementing populate_repl_namespace in its CLIPlugin.

Multi-REPL support

• stdlib REPL: python
• stdlib asyncio REPL: python -m asyncio (requires Python >= 3.13, since earlier versions to not allow customisation of the repl startup)
• IPython

The REPL can be selected by passing a value to --repl, e.g. litestar shell --repl=asyncio. If not value provided it will try to automatically select the best suited REPL:

• IPython if installed
• asyncio if >= Python 3.13
• Default REPL as a fallback

[codecov]

Codecov Report

❌ Patch coverage is 20.68966% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.79%. Comparing base (6ce617e) to head (8a445c3).

Files with missing lines	Patch %	Lines
litestar/cli/_utils.py	9.09%	10 Missing ⚠️
litestar/cli/_shell_startup.py	0.00%	6 Missing ⚠️
litestar/cli/commands/core.py	33.33%	6 Missing ⚠️
litestar/plugins/base.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4390      +/-   ##
==========================================
- Coverage   97.93%   97.79%   -0.15%     
==========================================
  Files         319      320       +1     
  Lines       15586    15614      +28     
  Branches     1726     1731       +5     
==========================================
+ Hits        15264    15269       +5     
- Misses        184      207      +23     
  Partials      138      138              

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[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/4390