Review #2517 for code improvements: LIMIT and OFFSET parameters written into the compiled query #2667

This is not a bug report. It is an invitation to look at #2517 again, because it keeps per-run values on the shared compiled statement. The goal is to understand the change and decide whether anything should be improved. The notes below come from a quick read of the diff, not from a full analysis.

The concern:

• The parameter value is written into the compiled query on every run. For LIMIT ? / OFFSET ? the statement function sets query.limit and query.offset from params at the start of each run (src/40select.js). The compiled query is shared by the statement cache and alasql.compile(), so two overlapping runs with different values can see each other's limit, the pattern described in Cached statements hold per-run state, so two runs of the same SQL at once overwrite each other #2596. Writing to query.limit at run time was also the cause of Set operation with ORDER BY / LIMIT on the first SELECT gives a different result from the second run #2605.
• Passing the limit and offset of the run to doLimit as values local to the run (resolved from params there) would leave the compiled query unchanged.

Related: #1381, #2596, #2605.