Har importer feature (complete) solves #122

[ayaan-md-blr]

PR Description

Complete implementation of har importer

Related Issues

• Closes Importing Requests from HAR file #122

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

har_parser/lib/test

• Yes
• No, and this is why: please replace this line with details on why tests have not been included

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux

[ashitaprasad]

Your proposal and code has gotten mixed up.