Lazy-load rich_utils to reduce startup time

[oefe]

Lazy-load rich_utils (and rich.traceback) to reduce import time.

Fixes #744

There was some discussion in that issue about using lazyasd and if TYPE_CHECKING: in order to make the import known to type checkers and build tools that perform import analysis.

To keep it simple, I didn't go that route.
There are already a few lazy imports, so I think this doesn't change the big picture.
And lazyasd appears to be no longer maintained.

Let me know if you rather would use lazyasd and/or if TYPE_CHECKING:.

Benefit

This cuts down startup overhead by 45%. Below are some measurements (best of 5 runs).
Measured on a Mac mini (M4 pro).

Before

~/R/typer►time uv run docs_src/first_steps/tutorial001.py
Hello World

________________________________________________________
Executed in   94.19 millis    fish           external
   usr time   71.72 millis    0.15 millis   71.57 millis
   sys time   19.54 millis    1.76 millis   17.77 millis

After

~/R/typer►time uv run docs_src/first_steps/tutorial001.py
Hello World

________________________________________________________
Executed in   51.99 millis    fish           external
   usr time   37.36 millis    0.10 millis   37.26 millis
   sys time   12.77 millis    1.37 millis   11.39 millis