[Portal] Docs: Fix detectMethod example (#5519)

CNCT-2479

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## PR-Codex overview
This PR updates the `detectExtension.ts` file to modify how the `detectMethod` function checks for the presence of the `decimals` method in a contract. It replaces the method signature with a specific selector.

### Detailed summary
- Changed the `detectMethod` call to use `availableSelectors: ["0x313ce567"]` instead of the method signature `"function decimals() view returns (uint8)"`.

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Author: gregfromstl

packages/thirdweb/src/utils/bytecode/detectExtension.ts

@@ -15,8 +15,8 @@ type DetectExtensionOptions = {
  * ```ts
  * import { detectMethod } from "thirdweb/utils/extensions/detect.js";
  * const hasDecimals = await detectMethod({
- *  contract,
  *  method: "function decimals() view returns (uint8)",
+ *  availableSelectors: ["0x313ce567"],
  * });
  * ```
  * @contract