doc: improve fs.StatFs documentation

[Jah-yee]

Good day

Summary

This PR improves the documentation for fs.StatFs class based on issue #50749.

Changes made:

1. Clarified bsize unit: Explicitly states that block size is in bytes (not bits)
2. Added examples for calculating space:
   • bavail: Example showing how to calculate available space in bytes
   • bfree: Example showing how to calculate free space in bytes
   • blocks: Example showing how to calculate total file system size in bytes
3. Improved files description: Clarified that it refers to inodes
4. Enhanced type documentation: Added explanation of what the type identifier represents and examples of common file system type values

Example additions:

import { statfs } from "fs/promises";

const stats = await statfs("/tmp");
const availableBytes = stats.bsize * stats.bavail;
console.log(`Available space: ${availableBytes} bytes`);

These changes help developers understand how to use the StatFs properties correctly, especially for calculating disk space.

Thank you for your attention. If there are any issues or suggestions, please leave a comment and I will address them promptly.

Warmly,
RoomWithOutRoof

[lpinca]

Duplicate of #62712.