Mock IO in writeLocalPackageList / writeOverrides ...

Mocking IO is required for writeLocalPackageList,
as we want to test the 'add-path' behavior.
While it is not a big concern for overrides, as they
are deprecated and we are unlikely to add new tests,
it is easy to do, and already done for reading them.

Remove the need to mock PackageManager.refresh() ...

We can finally test the full features of the base function,
as we are now mocking the IO, not the logic.

Remove direct IO from Location.scanLocalPackages ...

This is one more step towards removing our mocking of refresh_.

PackageManager: Mock readText, do not mock load ...

This allows us to test the behavior of the base class much better,
by overriding the last IO function, readText.

Move Package.findPackageFile to PackageManager, mock ...

Moving it to PackageManager allows us to call PackageManager.existsFile,
allowing us to mock a lot more things.

Remove the need for intermediate `.zip` file in PackageSupplier ...

By using a different overload of `retryDownload`,
we return the data instead of writing to disk,
ensuring that we don't have a lingering file
in memory and reducing IO.

This follow the same approach for deprecations as previous
`PackageSupplier` deprecations: it's an inevitable, but
easily fixable, breaking change for classes that implement
`PackageSupplier`, but it's a proper deprecation for client
code, based on the assumption that all the classes implementing
`PackageSupplier` are in Dub.

Fix ubyte[] download overload by avoiding a cast ...

We were using the default template parameter, `char`,
and as the documentation for `get` states:
> If asking for char, content will be converted from
> the connection character set (specified in HTTP
> response headers or FTP connection properties,
> both ISO-8859-1 by default) to UTF-8.

However we are downloading a binary so converting
it to UTF-8 will fail. Especially if we intend
to cast it to `ubyte[]` afterwards.

Trivial: Print the Exception message in retryDownload ...

This makes the source of the issue more obvious when using
the verbose flag.

Trivial: Upgrade remaining actions/checkout to v4 ...

Avoid deprecated Node 16.

Test: Directly mock writeFile/existsFile from PackageManager ...

This allows us to reduce the number of functions we override,
as we would like to test writeSelections and refresh directly,
not the copy of them we have.

Introduce FSEntry.removeFile, FSEntry.removeDir, refactor FSEntry.writeFile ...

Add the ability to remove directories and files,
and refactor writeFile to make this kind of function
easier to write.

Allow tests to call customCachePaths ...

This is now possible, as refresh has been mostly implemented.

Tests: Remove FSEntry.this dependency on TestDub ...

The dependency should always be the other way around (TestDub depends on FSEntry),
and this is an easy win to move.

Make FSEntry const and scope correct ...

This way we can use it in functions that are using
const/scope, like loadConfig.
As a minor improvement, the two `lookup` overloads
were moved next to one another.

Test: Move writePackageFile to UFCS, better document ...

This is another step in separating FSEntry from TestDub.

Merge both TestDub constructors ...

Those constructors had different but non-overlapping functionalities.
In the event one wanted to set one of the parameters passed to Dub
constructor but also initialize the FS, one was out of luck.

Remove FileInfo.timeCreated ...

As it is not available on all platforms, we can't really rely
on it for code, and it is indeed not used anywhere.

Tests: FSEntry.writeFile write to wrong directory ...

This was a subtle bug hidden by the fact that 'parent' exists
in the class. It was causing problems when calling 'print',
but luckily didn't affect anything else.

Test registry: Store version separate from Package ...

This will allow us to store full packages (FSEntry) instead of
the processed / already instantiated Package.

Introduce readText and make stripUTF8BOM private

Load dub.selections.json in unittest ...

Allow better testing by loading already resolved dependencies.

Merge pull request #2866 from Geod24/mlang/Simplify1 ...

Trivial: Simplify PackageManager's loadInternal

Move writing selections file to PackageManager ...

The PackageManager is the main source of IO in Dub,
and having it take responsibility for writing the
selections file reduces the number of special casing
we need to make when doing dependency injection.

Merge pull request #2865 from dlang/fix_issue_2691_reboot ...

Properly fix issue #2691 by reverting to the original scanning behavior

Simplify condition.

Trivial: Simplify PackageManager's loadInternal

Properly fix issue #2691 by reverting to the original scanning behavior. ...

Reverts to the scanning/warning behavior that was in place before the warnings for the new package directory structure were implemented.

Revert "Fix #2691: Use same structure for managed and unmanaged path" ...

This reverts commit 1a53049.

Remove an unused JSON serialization call ...

This was completely unused in the function.

Tests: Use TestDub FSEntry constructor for more accurate tests ...

The previous approach added Packages in the PackageManager directly,
completely sidestepping the scanning the PackageManager does,
which is a behavior we absolutely want to test.

By setting up the filesystem before we instantiate our `TestDub` instance,
we can remove a bunch of exceptions / overrides, and get a much closer
behavior to the final product.