Add --nextest-archive-file option to report subcommand

[taiki-e]

Support calling cargo llvm-cov report for the result of cargo llvm-cov nextest --archive-file.

cargo-llvm-cov/.github/workflows/ci.yml

Lines 86 to 88 in f9c7439

	cargo llvm-cov nextest-archive --archive-file a.tar.zst
	cargo llvm-cov nextest --archive-file a.tar.zst --text --fail-under-lines 70
	cargo llvm-cov report --nextest-archive-file a.tar.zst --fail-under-lines 70

cc @weiznich

Closes #350

[weiznich]

Thanks for picking up this work ❤️ . I unfortunately run out of time fixing the original PR 😞 .