Every request re-analyses the document, so latency grows with its size even without edits #95

Driving comline-lsp over stdio with one struct of N fields, the same hover twice in a row, with no edit in between, takes:

An unchanged document still costs seconds per request, growing linearly with its size, so the analysis appears to run per request rather than once per change. A single file that large is unusual, but analysis covers the whole package, so many files add up the same way, and every hover, completion and highlighting request pays it.

Fix: keep each document's analysis until it changes (and the package's until a file in it changes), and serve requests from it. Then a request costs the lookup, and only an edit costs analysis.

Measured on a debug build of main (bef0854).