Support busy timeout setting for SQLite driver

Some operations may not take place in parallel. In that case, by
default, SQLite will return a "database is locked" error. This creates
problems for multi-threaded applications that happen to do two such
operations at the same time. Most of the time, having one wait a little
while resolves the situation. The SQLite library makes this easy to set
up, providing a way to install a time-based busy handler.

This commit adds support for setting the busy timeout when creating a
new SQLite connection, and also defaults it to 10s, which will give a
much better experience to the average user who takes this module and
starts doing stuff with it from multiple threads. The previous default
(since we didn't call the `sqlite3_busy_timeout` function) was zero,
meaning that using multiple connection objects, one per thread, left
the user quite likely to run into the busy error.

lib/DBDish/SQLite.pm6

@@ -21,6 +21,9 @@ method connect(Str() :database(:$dbname)! is copy, *%params) {
 
     my $status = sqlite3_open($dbname, $p);
     if $status == SQLITE_OK {
+        given %params<busy-timeout> // 10000 {
+            sqlite3_busy_timeout($p, .Int);
+        }
         DBDish::SQLite::Connection.new(:conn($p), :parent(self), |%params);
     }
     else {

lib/DBDish/SQLite/Native.pm6

@@ -75,6 +75,11 @@ sub sqlite3_close(SQLite)
     is export
     { ... }
 
+sub sqlite3_busy_timeout(SQLite, int32)
+    returns int32
+    is native(LIB)
+    is export
+    { ... }
 
 sub sqlite3_prepare_v2 (
         SQLite,