Try absl::InlinedVector for speeding up Scorer::make_ngram et. al.

[reuben]

Seems like an easy win, just need to figure out the build aspects for the decoder Python package.

Before:

After:

[kdavis-mozilla]

0.8.0?

[reuben]

Not a big enough win to be a rush, and it's 100% an implementation detail, so we can land it after 1.0. I haven't made much progress on figuring out the ds_ctcdecode build stuff.