typing: create an @overload of `phasecache` ctor to handle the copy case In `phasecache.copy()`, it calls `self.__class__(None, None, _load=False)`, but the constuctor is typed to take a non-None repository. For the `_load=False` case, all args are ignored (and the copy function itself populates the attrs on the new object), so this isn't an error. For the default `_load=True` case, it needs a non-None repository. This is the simplest way to handle that duality. The reason this wasn't being detected is because pytype is confused by the interface decorators on the `localrepository` class, and is inferring the whole class as `Any`. (See 3e9a660b074a or c1d7ac70980b) Therefore, the type hint of `localrepo.localrepository` here was also effectively `Any`, which disabled the type checking entirely. This is the first foray into using `typing_extensions` to unlock future typing features. I think this is safe and reasonable because 1) it is only imported in the type checking phase (so no need to vendor our own copy), and 2) pytype has its own copy of `typing_extensions` bundled with it, so no need to alter the test environment. When run with a version of python that supports the symbol(s) natively, `typing_extensions` simply re-exports from `typing`, so there shouldn't be any future headaches with this.

typing: declare the `_phasesets` member of `phasecache` to be `Optional` Something in this area got flagged while making the repository class visible to pytype (instead of being typed as `Any`). A None assignment to something not optional is wrong, and when I tried setting it to `{}` to keep it non-Optional, some tests failed. There are checks for the attr being None elsewhere, so this seems to have just been an oversight.

typing: hide the interface version of `dirstate` during type checking As noted in the previous commit, the `dirstate` type is still inferred as `Any` by pytype, including where it is used as a base class for the largefiles dirstate. That effectively disables most type checking. The problems fixed two commits ago were flagged by this change. I'm not at all clear what the benefit of the original type is, but that was what was used at runtime, so I don't want to change the largefiles base class to the raw class. Having both a lowercase and camelcase name for the same thing isn't great, but given that this trivially finds problems without worrying about which symbol clients may be using, and the non-raw type is useless to pytype anyway, I'm not going to worry about it.

dirstate: remove the interface decorator to help pytype This is the same change that was made for some of the manifest classes in 3e9a660b074a. Note that `dirstate` is still inferred as `Any`, but at least we have `DirState` with all of the expected attributes.

largefiles: sync up `largefilesdirstate` methods with `dirstate` base class As it currently stands, pytype infers the `dirstate` class (and anything else decorated with `@interfaceutil.implementer`) as `Any`. When that is worked around, it suddenly noticed that most of these methods don't exist in the `dirstate` class anymore. Since they only called into the missing methods and there's no test failures, we can assume these are never called, and they can be dropped. In addition, PyCharm flagged `set_tracked()` and `_ignore()` as not overriding a superclass method with the same arguments. The missing default parameter for the former was the obvious issue. I'm guessing that the latter was named wrong because while there is `_ignore()` in the base class, it takes no arguments and returns a matcher. The `_ignorefiles()` superclass method also takes no args, and returns a list of bytes. The `_ignorefileandline()` superclass method DOES take a file, but returns a tuple. Therefore, the closest match is `_dirignore()`, which takes a file AND returns a bool. No idea why this needs to be overridden though.

sparse: reliably avoid writing to store without a lock With the code as written before this patch we can still end up writing to store in `debugsparse`. Obviously we'll write to it if by accident a store requirement is modified, but more importantly we write to it if another concurrent transaction modifies the requirements file on disk. We can't rule this out since we're not holding the store lock, so it's better to explicitly pass a permission to write instead of inferring it based on file contents.

debugsparse: stop taking the store lock debugsparse is a workspace-only opperation, or it better be workspace-only. Let's make it to stop taking the store lock.

scmutils: read the requires file before writing to avoid unnecessary rewrite This lets us get away without the repo lock in situations where we need to write requirements, but we know we're not changing the store requirements.

localrepo: remove _readrequires function in favor of scmutil.readrequires

scmutil: add `readrequires` next to `writerequires` The code is copied from localrepo.py.