feat: at_talk should use at_cli_commons.CLIBase and at_client.AtRpc

[gkc]

Is your feature request related to a problem? Please describe.

at_talk is a canonical demo but is not using the latest and greatest other pieces of software which reduce boilerplate and simplofy application code

Describe the solution you'd like

• replace how at_talk currently creates its AtClient instance by instead using CLIBase from the at_cli_commons package (example: https://github.com/atsign-foundation/at_libraries/blob/trunk/packages/at_cli_commons/example/bin/scan_example.dart)
• replace how at_talk currently sends and receives notifications by instead using AtRpc (example: https://github.com/atsign-company/gary-snippets/tree/main/at_rpc_demo)

Describe alternatives you've considered

No response

Additional context

No response