refactor(usage): shape sources as fetch functions

Keep the plugin usage API limited to stable report and presentation helpers. Source-local parsers and timeout handling preserve credential and response parity while the cases move alongside each source.

packages/plugin/src/server/usage.ts

@@ -1,4 +1,4 @@
-import { z, type ZodType } from "zod";
+import type { ZodType } from "zod";
 import type { JsonValue } from "@getpaseo/protocol/agent-types";
 
 export interface UsageWindow {
@@ -108,29 +108,6 @@ export function usedPctOf(
   return (used / limit) * 100;
 }
 
-export const ApiNumberSchema = z.coerce.number().finite();
-export const ApiNullableNumberSchema = z.preprocess(
-  (value) => (value == null ? null : value),
-  ApiNumberSchema.nullable(),
-);
-export const ApiOptionalStringSchema = z.preprocess(
-  (value) => (value == null ? undefined : value),
-  z.coerce.string().optional(),
-);
-
-export type UsageApiFetch = typeof fetch;
-
-export function fetchProviderApi(
-  fetchApi: UsageApiFetch,
-  input: RequestInfo | URL,
-  init: RequestInit = {},
-): Promise<Response> {
-  return fetchApi(input, {
-    ...init,
-    signal: init.signal ?? AbortSignal.timeout(15_000),
-  });
-}
-
 export function unavailableUsage(accountKey = "default"): UsageReport {
   return {
     account: { key: accountKey },
@@ -140,8 +117,3 @@ export function unavailableUsage(accountKey = "default"): UsageReport {
     details: [],
   };
 }
-
-export function toIsoStringOrNull(timestampMs: number): string | null {
-  const date = new Date(timestampMs);
-  return Number.isFinite(date.getTime()) ? date.toISOString() : null;
-}