[docs] Update README roadmap to reflect implemented features

[AryanSharma48]

Problem

The main README contains a roadmap showing features that are planned or
completed.

Some features that are already implemented are still marked as incomplete.

In particular:

• Request timeout support
• AbortController integration

are currently shown as unchecked even though the functionality exists in
the project.

What needs to be done

Review the relevant implementation and update the README roadmap so that
implemented features are correctly marked as completed.

Acceptance Criteria

• Request timeout support is marked as completed
• AbortController integration is marked as completed
• No unrelated roadmap items are changed
• README formatting remains consistent

Files to look at

• README.md
• packages/smooth-api-ts/src/index.ts

Prerequisites

Basic Markdown.

Notes

Before changing the roadmap, verify that the features are actually
implemented in the codebase.