add duckdb-ui-client & other ts pkgs (#10)

* add duckdb-ui-client & other ts pkgs

* workflow fixes

* fix working dir

* no sparse checkout; specify package.json path

* path to pnpm-lock.yaml

* add check & build test

* workflow step descriptions

* use comments & names

* one more naming tweak

ts/pkgs/duckdb-data-values/src/DuckDBTimestampSecondsValue.ts

@@ -0,0 +1,20 @@
+import { getDuckDBTimestampStringFromSeconds } from './conversion/dateTimeStringConversion.js';
+import { Json } from './Json.js';
+import { SpecialDuckDBValue } from './SpecialDuckDBValue.js';
+
+export class DuckDBTimestampSecondsValue extends SpecialDuckDBValue {
+  public readonly seconds: bigint;
+
+  constructor(seconds: bigint) {
+    super();
+    this.seconds = seconds;
+  }
+
+  public toDuckDBString(): string {
+    return getDuckDBTimestampStringFromSeconds(this.seconds);
+  }
+
+  public toJson(): Json {
+    return this.toDuckDBString();
+  }
+}