* chore: drop redundant numeric import aliases
Refactoring left behind import aliases like `datasync2`/`types3` that
just repeat the package name. Remove them where the plain package name is
unambiguous in the file, and drop three duplicate imports of the same path.
* chore: name colliding type imports after repo convention
Where two packages named `types` (or `rpc`) meet in one file an alias is
unavoidable, so use the descriptive names already dominant in the tree
(cryptotypes, messagingtypes, wakutypes, accsmanagementtypes, wsdktypes,
noderpc) instead of types2/types3/rpc2, and spell the messaging/waku
import wakuv2 everywhere (was wakuv/wakuv2/wakuv3).
* chore: rename package wakuv2 to waku
The package in pkg/messaging/waku still declared itself `wakuv2`, which
forced every import site to carry an alias (goimports re-adds one when the
package name differs from its directory). Rename the package so the import
can stand as-is, and rename the local `waku` variable in transport_test.go
to `wakuNode` to free up the name.
* chore: unalias protocol/contacts import in protocol tests and backup
`contacts2` was only needed because local variables took the package name.
Rename those to what they hold — syncContacts for the sync messages built in
backupContacts, addedContacts/allContacts in the contact request and
verification tests — and import the package as-is.
Igor Sirotin