Hide version info in pixi search -l 0 output

[mvanhorn]

When the version limit is set to 0 (-l 0), only bare package names are
printed - no version counts, no version lines, no "more versions" hints.

Before:

> pixi search cargo* -l 0
cargo-audit (15 versions)
... and 15 more versions (use -l to show more)

cargo-auditable (8 versions)
... and 8 more versions (use -l to show more)

After:

> pixi search cargo* -l 0
cargo-audit
cargo-auditable
cargo-binutils
cargo-bundle-licenses
cargo-c

This gives a clean list suitable for piping or scripting.

Fixes #5763

[baszalmstra]

Superseded by #5820