Is there a reason for masquerading the notify features? We simply let user specify them in their own cargo toml until now.

In the past, debouncers used notify with default features, including crossbeam-channel and macos_fsevents -- even if default features were disabled by the user on both the debouncer and the notify direct dependency.

Users were effectively unable to disable crossbeam-channel on notify when using a debouncer.

This change sets the debouncers' notify dependency to default-features = false, to allow users to even disable them at all.

However, leaving it at that would break compatibility for MacOS users, as macos_fsevent would no longer be enabled by default.

Therefore, this change to the debouncers' feature set makes notify's default features their own, to keep the existing behavior, where debouncers with default features include notify with default features.

Some details - skip if you like:

The reasoning has two parts: 1. Not breaking MacOS use by enabling macos_fsevent by default, as it used to be, and 2. convenience of pass through for ease of configuration for library users.

1. I made this change so that a missing macos_fsevent does not break MacOS use where notify default features used to be enabled when using a debouncer:
   
   The debouncers now disable notify's default features to fix the described issue.
   
   However, this causes macos_fsevents to be disabled by default. For compatibility, it needs to be kept enabled.
   
   Therefore, the debouncers need to include macos_fsevent in their default features.
   
   As a library user, I would want notify default features (crossbeam-channel + macos_fsevent) to work as they did before, but be able to disable them.

2. I made this change so that macos_fsevent and macos_kqueue can make use of the convenient feature pass-through which had previously been available only for crossbeam-channel:
   
   If a MacOS user depends on one of the debouncers, they can define e.g. notify-debouncer-full = { version = "*", default-features = false, features = ["macos_kqueue"] } without having to add notify as a direct dependency.
   
   The debouncers' and the underlying notify's features must match (see crossbeam feature). The easiest way to make them match is to make users define them only on the debouncers.
   
   If the macos_fsevent pass-through is removed (Breaking!), then probably the macos_kqueue and crossbeam (Breaking!) pass-through features should be removed as well.
   
   To my mind, it seems intransparent and error prone to require users to add a second explicit dependency just to enable some feature flags. As a library user, I would prefer to have all three pass-throughs available.