Add test coverage for cmd/oras/internal/display

[TerryHowe]

Add test coverage for cmd/oras/internal/display packages. Create a pull request and include "Partial: https://github.com/oras-project/oras/issues/1916" as a line in the description. Check the box when it merges. Check that an existing PR does not exist before creating one. Thanks!

• [ ] oras.land/oras/cmd/oras/internal/display/content/discard.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/content/manifest_fetch.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/content/manifest_index.go 75.0%
• [ ] oras.land/oras/cmd/oras/internal/display/handler.go 36.7%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/descriptor/manifest_fetch.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/discard.go 42.9%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/attach.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/discover.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/manifest_fetch.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/pull.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/push.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/repo_list.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/json/repo_tags.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/attach.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/descriptor.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/discover.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/fetched.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/pull.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/push.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/repo_list.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/repo_tags.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/model/tag.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/attach.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/discover.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/manifest_fetch.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/pull.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/push.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/repo_list.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/template/repo_tags.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/manifest_delete.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/manifest_index.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/manifest_push.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/pull.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/push.go 25.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/repo_list.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/metadata/text/repo_tags.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/status/console/console.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/status/discard.go 17.9%
• [ ] oras.land/oras/cmd/oras/internal/display/status/progress/humanize/bytes.go 62.5%
• [ ] oras.land/oras/cmd/oras/internal/display/status/progress/manager.go 75.3%
• [ ] oras.land/oras/cmd/oras/internal/display/status/text.go 56.1%
• [ ] oras.land/oras/cmd/oras/internal/display/status/track/reader.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/status/track/target.go 0.0%
• [ ] oras.land/oras/cmd/oras/internal/display/status/tty.go 48.3%

Related https://github.com/oras-project/oras/issues/1461