Add classic L2CAP connection conveniences

[colemancda]

Summary

Adds classic (BR/EDR) counterparts to the existing Low Energy L2CAP conveniences:

• L2CAPSocket.classicClient and L2CAPSocket.classicServer — PSM-based connections using the ProtocolServiceMultiplexer enum (SDP, RFCOMM, BNEP, HID control/interrupt, AVDTP, and others), with CID 0 and no LE address type. Async HostController overloads read the adapter address automatically.
• Matching wrappers on L2CAPSocket.Server and L2CAPSocket.Connection.
• The non-blocking connect-and-poll logic is factored into a shared internal helper.

This is the missing transport piece for Personal Area Networking (#57) and unblocks future HID and SDP work.

Test plan

• 3 new unit tests verifying classic and LE socket address encoding and decoding (PSM byte order, CID, address type). Socket address construction requires the Bluetooth address family, which is Linux-only, so these are gated to run in CI rather than on Darwin.
• Full test suite passes
• swift build succeeds with no new warnings
• Live connections require Linux with a Bluetooth adapter