fix(opencode-go): add qwen plus tiered pricing (#91351)

* fix(opencode-go): add qwen plus tiered pricing

* fix(usage): tier pricing by total prompt tokens

* fix(pricing): select qwen tiers by prompt tokens

* fix(pricing): preserve tier basis across catalogs

* fix(opencode-go): keep qwen pricing representable

---------

Co-authored-by: Vincent Koc <vincentkoc@ieee.org>

extensions/opencode-go/index.test.ts

@@ -182,6 +182,12 @@ describe("opencode-go provider plugin", () => {
     expect(qwen37Plus.reasoning).toBe(true);
     expect(qwen37Plus.contextWindow).toBe(1_000_000);
     expect(qwen37Plus.maxTokens).toBe(65_536);
+    expect(qwen37Plus.cost).toMatchObject({
+      input: 0.4,
+      output: 1.6,
+      cacheRead: 0.04,
+      cacheWrite: 0.5,
+    });
 
     const dynamicModel = requireRecord(
       provider.resolveDynamicModel?.({