feat(fluxtest): enhance fluxtest to use package name with test/skip flags

[skartikey]

The package name can be added to the testcase name as a qualifier
Format - package.name

Here is an example -
There are 2 testcase exist with name group

$find . -name '*.flux' | xargs grep 'testcase group '
./stdlib/experimental/group_test.flux:testcase group {
./stdlib/universe/group_test.flux:testcase group {

// testcase name without qualifier will run both the test.

go run ./cmd/flux test --test group

// testcase name with qualifier will run the specific test

go run ./cmd/flux test --test universe.group
go run ./cmd/flux test --test experimental.group

Adding a duplicate test name in the same package will produce an error -
testcase name "group", already exists in package "universe"

fixes: #4877

Checklist

Dear Author 👋, the following checks should be completed (or explicitly dismissed) before merging.

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• 🏃 Test cases are included to exercise the new code
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[wolffcm]

I had some comments but this looks good for the most part. I had a couple of comments that it would be good to address.

Let's make sure that downstream repos, which have their own skip lists, continue to work right.

[wolffcm]

You are definitely close on this, but it would be good to have test case for the error that is produced when two cases have the same name in the same package. That will keep us from having any ambiguity moving forward, to it would be good to lock it down.

[skartikey]

After merging #5057 Did a manual test by duplicating the test case name in the same package and got the below error -

duplicate testcase name "group", found in package "universe", at locations stdlib/universe/group_test.flux|38:10-38:15 and stdlib/universe/group_ungroup_test.flux|48:10-48:15

[wolffcm]

Very nice!