Fix graininess & streaks for 7.50inV2alt Waveshare e-paper

[Egglestron]

This fix is based on demo files provided by Waveshare.

What does this implement/fix?

It resolves the graininess and streaking of previous versions of the library.
esphome/issues#2216

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes esphome/issues#2216

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040

Example entry for config.yaml:

# Example config.yaml
external_components:
  - source:
      type: git
      url: https://github.com/egglestron/esphome
      ref: dev
    components: [ waveshare_epaper ]

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[jesserockz]

Please don't comment out code, just remove it.

[jesserockz]

Merging based on peoples comments on the linked issue