[Parallel] Engine: Change some strict evaluations

1. Using ($!!) instead of deepseq

2. Forcing the evaluation of the ocurrenceMap instead of the newIndex
on the processFile' function. This way avoids unnecessary computation
traversing all the index (some indices already were evaluated). Maybe
next step will be to create a new index using only the occurrences read
from the current file, force its evaluation and then merge with the
index on the buffer to create a new one.

3. Creating the query index on a separate thread. There is no need to
block the file processing thread during the query index creation.