Have consistent naming for imported SDK and internal packages

[roman-khimov]

Is your feature request related to a problem? Please describe.

I'm always frustrated when the same packages can be named differently in the codebase. One of the sources of this trouble is that we have similarly named packages from SDK and node codebases, then in some cases the original name is used for SDK package, in some cases it's used for internal one, or we can have prefixes or suffixes added arbitrarily. For example, github.com/nspcc-dev/neofs-sdk-go/netmap is known as netmap, netmapsdk, sdknetmap, netmapSDK and then github.com/nspcc-dev/neofs-node/pkg/core/netmap can be known as netmap, netmapcore, corenetmap or netmapCore. This is very annoying.

Describe the solution you'd like

Follow simple rules set by 4c71c2d and b17da10:

• SDK packages are never renamed, always imported as is
• packages from local pkg/core prefix are named and imported with core suffix, so for pkg/core/netmap netmapcore is the name of the package used everywhere
• packages from github.com/nspcc-dev/neofs-sdk-go/proto/ are imported with proto prefix, like protoobject, protostatus, etc.

Describe alternatives you've considered

No alternatives.

Additional context

#3748.

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[carpawell]

Why netmapcore but protonetmap (the order)?

[roman-khimov]

Just because that's the way it is now.