Refactor Task Internal Modules: Channels

[charitylxy]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

This PR aims to address issue brought up in #461:

• Currently, task subobject types are defined in internal modules contained in private nidaqmx._task_modules package.
• We want to turn task.py into a package and merge it with the internal modules contained in nidaqmx._task_modules

Refactoring work will be split into 5 PRs:

• Refactoring _task.py and _in_stream.py - Refactor task.py and internal module (in_stream.py)  #534
• Refactoring _export_signal.py, _out_stream.py, _timing.py - Refactor Task Internal Modules (ExportSignal, OutStream, Timing) #539
• Refactoring collections: _channel_collection.py, _ai_channel_collection.py, _ao_channel_collection.py, _ci_channel_collection.py, _co_channel_collection.py, _di_channel_collection.py, _do_channel_collection.py - Refactor Task Internal Modules: Collections #541
• Refactoring channels: _channel.py, _ai_channel.py, _ao_channel.py, _ci_channel.py, _co_channel.py, _di_channel.py, _do_channel.py
• Refactoring triggering: _triggers.py, _arm_start_trigger.py, _handshake_trigger.py, _pause_trigger.py, _reference_trigger.py, _start_trigger.py

Why should this Pull Request be merged?

In this PR to address #461, following changes have been made:

• Moved channels to task package and made its modules private.
• Imported the updated metadata from grpc-device-scrapigen to have the new module name documented.
• Documentation updated
• tests/component/_task_modules renamed to tests/component/task.
• Modified the affected module names in tests.

What testing has been done?

Ran poetry run pytest and all tests passed.

[zhindes]

defer to Brad

[bkeryan]

Looks good, thanks!