library: vendors/sqlite — SQLite ships with sx

The vendored amalgamation (3.53.2, public domain) plus the curated
bindings move from the distribution repo into the sx library:
'#import "vendors/sqlite/sqlite.sx"' gives any sx program SQLite
with no system dependency and no build flags — the bindings declare
the C as a named #import c unit (pinned defines + -O2), compiled
through the object cache and shadow-proof via unit-first resolution.
examples/1624 pins the version and a typed round trip in-suite.

examples/expected/1624-vendor-sqlite-module.exit

@@ -0,0 +1 @@
+0

examples/expected/1624-vendor-sqlite-module.stdout

@@ -0,0 +1,2 @@
+row: b 2
+vendored sqlite 3.53.2 ok