feat: add custom separators, read reciepts, timestamp with read status

[creepysta]

Important -

• expose a list of custom separators in message_list_options
• expose onTapDown for GestureDetector in message_options for noting the user touch offset on the screen

Others -

• Implement message timestamp in the message_container with Stack to show the timestamp in the same line if the message is short.

Related Issue - #60
main PR - #59