Update pubspec.yaml to losen better_networking sdk constraints

[Aman071106]

PR Description

This PR fixes the issue caused in developer experience due to loosen dependency constraint for better_networking_package which required dart 3.8.0 minimum SDK version. The details are addressed in Issue #875.

Related Issues

• Closes Fix SDK constraint mismatch in pubspec.yaml (DX: setup issue) #875

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?

• Yes
• No, and this is why: This PR only updates the SDK constraints. No functional changes that require tests.

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux