bpo-42862: Use functools.lru_cache iso. _sqlite.Cache in sqlite3 module

Doc/library/sqlite3.rst

@@ -213,7 +213,7 @@ Module functions and constants
    The :mod:`sqlite3` module internally uses a statement cache to avoid SQL parsing
    overhead. If you want to explicitly set the number of statements that are cached
    for the connection, you can set the *cached_statements* parameter. The currently
-   implemented default is to cache 100 statements.
+   implemented default is to cache 128 statements.
 
    If *uri* is true, *database* is interpreted as a URI. This allows you
    to specify options. For example, to open a database in read-only mode

Misc/NEWS.d/next/Library/2021-01-13-00-02-44.bpo-42862.Z6ACLN.rst

@@ -0,0 +1,4 @@
+:mod:`sqlite3` now utilizes :meth:`functools.lru_cache` to implement the
+connection statement cache. As a small optimisation, the default
+statement cache size has been increased from 100 to 128.
+Patch by Erlend E. Aasland.