Improve exception handling in Flodesk::Client

[mikej]

Currently we've got the following code in Client#request:

planner/lib/flodesk.rb

Lines 128 to 133 in 45fd9d1

	rescue Faraday::Error => e
	FlodeskError.new(e.response_body['message'], {
	raw_body: e.response_body,
	status_code: e.response_status
	})
	end

Make code nil-safe

This can result in a NoMethodError: undefined method '[]' for nil if there is an issue connecting to Flodesk and the response doesn't actually contain a message_body.

This could happen in production, but also can be a source of flaky tests as happened recently.

Proposing to make this nil-safe by using e.response_body&.['message']

Raise rather than return the exception

Currently this code is actually returning the FlodeskError rather than raising it.

Proposing to raise the exception instead, but note there's one place where we currently check the return type from the method that will need updating to reflect this change:

planner/lib/flodesk.rb

Lines 70 to 74 in 45fd9d1

	def subscribed?(email:, segment_ids:)
	response = request(:get, "subscribers/#{email}")
	response => { status:, body: }
	return false if response.is_a?(FlodeskError) && status == 404

Mock out the client in tests

As a separate task we can take a look at mocking Flodesk::Client in the specs.