feat: updated incorrect description of the current network phase

Updated documentation to correct inaccuracies regarding the network description. Changed instances referring to the network as the testnet to accurately reflect the mainnet status. This ensures consistency between the documentation and the actual network deployment, preventing confusion for users.

Details:

Updated all relevant sections in the documentation.
Verified the accuracy of the changes against the current mainnet status.
No structural changes were made, only corrections to network descriptions.
Thank you for reviewing and merging!

Author: zm-moon

src/content/docs/en/developers/index.mdx

@@ -86,6 +86,6 @@ ensuring that all code executed on the Scroll Layer 2 behaves just as if it were
 
 ## Thank you for building with us.
 
-We’re working to bring more integrations and support infrastructure to the network, and are excitedly working towards our Mainnet release.
+Our mainnet is now live, and we're diligently working to bring more integrations and support infrastructure to the network.
 
 Join our growing developer community. You can find us on [Discord](https://discord.gg/scroll), join our [discussion forum](https://community.scroll.io/), or follow our progress on [Twitter](https://twitter.com/Scroll_ZKP).