Updates

[luispabon]

Changes:

• Update to php 8
• Update symfony/console to 5.3
• Update to latest infection
• Tweak build to use the newest most strict phpstan level (7 --> 8)
• Update code and tests to take advantage of php 8 features:
  • Constructor property promotion
  • Certain property types (mixed etc)
  • Remove redundant docblocks specifying types
• Update guzzle from v6 to v7:
  • BadRequestException can no longer return null on the response, so simplify code that dealt with this & tests to reflect it.
  • Tweak some http client mocks where responses were returned as null to return mock responses