PostgreSQL for Bjolang: bjosql over Npgsql, for bjoroutines

Every operation suspends its fiber while it waits for the server, and
the ambient cancellation token cancels the query. A Db is a pool; a
transaction holds one connection and hands its function a Db bound to
it, and a nested one is a savepoint. Each SqlValue is a typed parameter,
and a value is read back by the PostgreSQL type of its column. The
server's errors are DbError with its SQLSTATE, and a lost connection is
DbError 08000.

🤖 Generated with [ECA](https://eca.dev)

Co-Authored-By: eca-agent <git@eca.dev>

.gitignore

@@ -0,0 +1,8 @@
+.bjo/
+*.dll
+*.exe
+*.pdb
+*.bjobuild
+*.runtimeconfig.json
+*.deps.json
+*.db