docs: Miscellaneous doc fixes in attribute + unit tests #942

Job	Run time
golangci-lint	35s
terraform-provider-corner (tfprotov6 / Terraform 1.0.*)	57s
terraform-provider-corner (tfprotov5 / Terraform 0.12.*)	35s
test (Go v1.22)	27s
terraform-provider-corner (tfprotov6 / Terraform 1.1.*)	44s
terraform-provider-corner (tfprotov5 / Terraform 0.13.*)	43s
test (Go v1.21)	45s
terraform-provider-corner (tfprotov6 / Terraform 1.2.*)	44s
terraform-provider-corner (tfprotov5 / Terraform 0.14.*)	57s
terraform-provider-corner (tfprotov6 / Terraform 1.3.*)	39s
terraform-provider-corner (tfprotov5 / Terraform 0.15.*)	59s
terraform-provider-corner (tfprotov6 / Terraform 1.4.*)	44s
terraform-provider-corner (tfprotov5 / Terraform 1.0.*)	50s
terraform-provider-corner (tfprotov6 / Terraform 1.5.*)	54s
terraform-provider-corner (tfprotov5 / Terraform 1.1.*)	45s
terraform-provider-corner (tfprotov6 / Terraform 1.6.*)	41s
terraform-provider-corner (tfprotov5 / Terraform 1.2.*)	40s
terraform-provider-corner (tfprotov6 / Terraform 1.7.*)	53s
terraform-provider-corner (tfprotov5 / Terraform 1.3.*)	47s
terraform-provider-corner (tfprotov6 / Terraform 1.8.*)	58s
terraform-provider-corner (tfprotov5 / Terraform 1.4.*)	35s
terraform-provider-corner (tfprotov6 / Terraform 1.9.*)	1m 0s
terraform-provider-corner (tfprotov5 / Terraform 1.5.*)	39s
terraform-provider-corner (tfprotov5 / Terraform 1.6.*)	54s
terraform-provider-corner (tfprotov5 / Terraform 1.7.*)	43s
terraform-provider-corner (tfprotov5 / Terraform 1.8.*)	58s
terraform-provider-corner (tfprotov5 / Terraform 1.9.*)	56s
	21m 2s

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