Fix race condition on getIsSchemaDatabase cache

We a client instance is used concurrently before the
isSchemaDatabasePromise is resolved, this led to multiple executions
of the underlying function. It should only be executed once, and the
promise should be shared among callers, which is what this change
enables.

packages/libsql-client/src/http.ts

@@ -71,7 +71,7 @@ export class HttpClient implements Client {
     protocol: "http";
     #url: URL;
     #authToken: string | undefined;
-    #isSchemaDatabase: boolean | undefined;
+    #isSchemaDatabase: Promise<boolean> | undefined;
 
     /** @private */
     constructor(
@@ -87,9 +87,9 @@ export class HttpClient implements Client {
         this.#authToken = authToken;
     }
 
-    async getIsSchemaDatabase(): Promise<boolean> {
+    getIsSchemaDatabase(): Promise<boolean> {
         if (this.#isSchemaDatabase === undefined) {
-            this.#isSchemaDatabase = await getIsSchemaDatabase({
+            this.#isSchemaDatabase = getIsSchemaDatabase({
                 authToken: this.#authToken,
                 baseUrl: this.#url.origin,
             });

packages/libsql-client/src/ws.ts

@@ -124,7 +124,7 @@ export class WsClient implements Client {
     #futureConnState: ConnState | undefined;
     closed: boolean;
     protocol: "ws";
-    #isSchemaDatabase: boolean | undefined;
+    #isSchemaDatabase: Promise<boolean> | undefined;
 
     /** @private */
     constructor(
@@ -142,9 +142,9 @@ export class WsClient implements Client {
         this.protocol = "ws";
     }
 
-    async getIsSchemaDatabase(): Promise<boolean> {
+    getIsSchemaDatabase(): Promise<boolean> {
         if (this.#isSchemaDatabase === undefined) {
-            this.#isSchemaDatabase = await getIsSchemaDatabase({
+            this.#isSchemaDatabase = getIsSchemaDatabase({
                 authToken: this.#authToken,
                 baseUrl: this.#url.origin,
             });