Consider not showing PyPy downloads in `uv python list` by default

[zanieb]

I sort of wonder if we want to be showing all those PyPy interpreters by default? Most users don't need them.

We do already show them if you request pypy

❯ uv python list pypy
pypy-3.11.11-macos-aarch64-none    <download available>
pypy-3.10.16-macos-aarch64-none    <download available>
pypy-3.10.14-macos-aarch64-none    /opt/homebrew/bin/pypy3 -> ../Cellar/pypy3.10/7.3.17_1/bin/pypy3
pypy-3.9.19-macos-aarch64-none     <download available>
pypy-3.8.16-macos-aarch64-none     <download available>

Originally posted by @zanieb in #12915 (comment)