Not threadsafe (or possibly even async-safe) on Julia 1.10

[kleinschmidt]

For julia 1.11+, the list of active patches (the patch env) is stored in a ScopedValue, which makes it safe to apply inside tasks, even when those tasks are scheduled on different threads and executing concurrently. For earlier versions, the patch env is stored in a package global Ref, which is definitely not concurrency friendly lol.

IIUC, the reason we're not using the ScopedValues.jl fallback is because it uses the logging machinery on julia <1.11 to smuggle in scoped values, and this in turn interferes with the test logger that @test_logs uses to, you know, test logging.

It seems really bad to me that there's silently, inconsistently thread-unsafe application of patches in some versions of julia but not others. I'd rather we allow users to opt out of using the ScopedValues fallback if they need to. I think it would be possible to allow users to control whether a global ref is used or a scoped value with a configuration option, like a boolean flag ref that can be set.

[omus]

The original thinking on this was to let newer versions of Julia use the newer features. However, inconsistent behavior between different versions of Julia is asking for trouble. I see two ways out of this mess:

1. Release new versions of Mocking.jl which require newer versions of Julia for the features that require it. I want to keep supporting the LTS so I think I would end up supporting a version for the LTS, 1.11+ (ScopedValues support), and 1.12+ (ability to drop @mock on call sites).
2. Introduce a "strategy" global which allows the user to choose between the Ref approach, ScopedValues, or ScopedValues without @mock). If the user attempts to use a strategy which isn't supported by that version of Julia we can throw an error. The main issue with this would be maintainability of the code base.

I think option 2 would be better if we can support it.

There is also a challenge with what to do with the current inconsistent behavior. With option 2 I think I'd have a "inconsistent" strategy which keeps the current behavior as the default. I could also make a new breaking release which possible uses the best strategy and forces users to opt into another strategy if they want to use that version of Julia with Mocking.