While testing performance improvements elsewhere, I noticed some
micro-optimizations could give a small ~2-3% speedup in my test
using the git async API to parse a large inbox.
The `read' perlfunc already has read-in-full behavior (unless
git is killed unexpectedly), so there's no point in using a
loop. SearchIdxShard in the parallel v2 indexing code path
never looped on `read', either.
Furthermore, we can avoid method dispatch overhead on ->getline
and ->print by using `readline' and `print' as ops which can be
resolved during the Perl compilation phase.
Finally, avoid passing the IO handle around as a parameter,
since avoiding hash lookups with a local variable has its own
costs in stack and refcount bumping.