* v2 client scaffolding

* gomod: go-libp2p-core and go-libp2p-transport-upgrader feature dependencies

* Conn implements network.ConnStat

* add reservation stub

* utilities

* dial scaffolding and v1 compat dialing

* stream handling scaffolding and v1 incoming connection handling

* implement hop tagging

* export timeout variables

* v2 protobuf

* v2 client protocol implementation

* implement Reserve

* go get go-libp2p-swarm@feat/transient-conns

* implement client.New

* rework pb status codes

* client responds with UNEXPECTED_MESSAGE when it's actually an unexpected message

* relay scaffolding, reservation implementation

* implement relaying

* implement missing details

* add options for resources/limit

* gc idle conn counts

* fix clown shoes in cancellation check

* end to end relay test

* untag peers with expired reservations

* add time limit test

* better debug log for accepted conns

* add data limit test

* add v2-v1 compatibility tests

* godocs

* add WithACL relay option

* only return public relay addrs in reservation record

* remove the refresh restriction madness

* set default limit Data to 128K

* fix typo in AllowReserve godoc

* fix some small issues

- remove context from constructor
- remove stream handler when closing the host
- remove the awkward cancellation check from handleStream

* fix tests

* address review comments

- Add deadline for Reserve calls
- Add deadline for dials
- Add some comments for things that confuse aarsh.

* humor aarsh and add initializers for slices

* comment nitpicks

* fix bug in slice pre-allocations

* add deadline to connectV1

* make Relay.Close thread-safe

* untag peers with reservations when closing the relay

* gomod: get go-libp2p-asn-util

* add IP/ASN reservation constraints

* gomod: update deps

* fix e2e test

* increase default limit duration to 2min

* update protocol for vouched relay addrs; provide absolute expiration time instead of TTL

* update for reservation changes

* add voucher to the reservation pb

* TODO about reservation vouchers

* deduplicate protocol ID definitions between relay and client

* add reservation vouchers

* emit and consume reservation vouchers

* improve limit data test

* deduplicate concurrent relay dials to the samke peer

* improve dialer deduplication

* add a short timeout to dialing the relay in order to aid deduplication

* gomod: fix go1.16 madness

* spec compliance: don't include p2p-circuit in reservation addrs

* spec compliance: refuse reservation and connection attempts over relayed connections

* test shim: add empty file in test directory

* spec compliance: update protobuf

* spec compliance: use libp2p envelopes for reservation vouchers

* fix staticcheck

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

simplify generation of reservations

* base limits on reservations issued

* switch default reservation limits per peer and per IP

* don't export the constructor for relay.constraints

* panic when reading from crypto/rand fails

* optimize IP-based reservation lookup

* use lists instead of maps to save reservations

* save expiry timestamp in reservations

* use slices instead of linked lists for reservations

* remove unused rand in constraints