Feat: intermediary commit (bundle processor)

packages/datastructure/lru_cache.go

packages/model/bundle/bundle.go

packages/model/bundle/hasher.go

packages/model/meta_transaction/meta_transaction.go

packages/model/meta_transaction/meta_transaction_test.go

packages/model/transactionmetadata/transactionmetadata.go

packages/model/valuebundle/metabundle.go

plugins/bundleprocessor/errors.go

plugins/bundleprocessor/events.go

plugins/bundleprocessor/plugin.go

plugins/tangle/bundle.go