chore(deps): bump vendored nbio to v1.6.11 (and llib to v1.2.3)

[moralpriest]

Summary

Prep work for a future Go toolchain bump: upgrade the vendored nbio
(mining/getwork websocket server) from the community-dev-pinned version to
v1.6.11.

nbio v1.6.11's nbhttp code imports lesismal/llib/std/crypto/tls, so
llib is bumped in lockstep from ~v1.1.4 to v1.2.3.

Consumer changes — cmd/derod/rpc/websocket_getwork_server.go

nbio v1.6.11 changed two APIs the daemon uses:

• websocket.Conn is now a concrete type (was an interface) → dropped the
  conn.(*websocket.Conn) assertion.
• OnReadBufferAlloc / OnReadBufferFree callbacks now take *[]byte
  (matching nbio v1.6.11's Allocator API) → updated the mempool
  callbacks accordingly.

No change to daemon getwork behavior or protocol.

Vendored upstream fix

llib v1.2.3 has a nil-pointer panic in non-blocking TLS mode: its deferred
conn.close dereferences c.rawInput without a nil check. nbio v1.6.11 forces
TLS on the server, so this path is always hit. Applied a one-line nil-guard at
vendor/github.com/lesismal/llib/std/crypto/tls/conn.go:
if c.rawInput != nil && len(*c.rawInput) == c.rawInputOff { ... }.

Tests

• cmd/derod/rpc/nbio_websocket_test.go — Go unit test exercising a real
  nbhttp server (HTTP→websocket upgrade, echo round-trip, connection
  lifecycle, TLS handshake through the llib fix). Passes.
• tests/normal/nbio_getwork_test/run_test.sh — boots a real derod --testnet
  (which starts the getwork server on nbio) and a real dero-miner
  (gorilla/websocket client); verifies the miner connects and receives work
  with no Error connecting. Passes.

Scope notes

• go.mod stays at go 1.17 — this is prep only, no toolchain bump.
• Pure vendored source swap (community-dev convention: no go.mod requires,
  no vendor/modules.txt, no go.sum).
• The simulator-based run_integration_test.sh suite does not exercise the
  getwork/nbio path, so it is out of scope; the change is isolated to the
  getwork server and its vendored deps.