Rename version to dolt_version (and return the doltlite version)

Keep every Dolt version-control helper dolt_-prefixed. The old #version was
both unprefixed and wrong: it returned the SQLite libversion. dolt_version now
returns SELECT dolt_version(). Generic connection methods (open/execute/query/
close) stay unprefixed as ordinary SQLite operations.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: timsehn

lib/doltlite/database.rb

@@ -51,8 +51,9 @@ def dolt_commit(message:, all: true)
       rows.dig(0, 0)
     end
 
-    def version
-      C.sqlite3_libversion
+    # The doltlite version string (SELECT dolt_version()).
+    def dolt_version
+      execute("SELECT dolt_version()").dig(0, 0)
     end
 
     def close