Migrate HCICommandParameter encoding to DataContainer

[colemancda]

What changed

Finishes the encode-side DataContainer migration for the HCI layer (#161), the counterpart to #206 for BluetoothGATT.

• HCICommandParameter now requires the generic func append<Data: DataContainer>(to:) instead of Foundation's var data: Data, and HCIPacketHeader (command/event headers) gets the same treatment. DataContainer gains init<T: HCICommandParameter>(_:) and init<T: HCIPacketHeader>(_:) for building buffers.
• All 91 command/header encoders migrated to the generic API. Types that were already DataConvertible (e.g. HCILECreateConnection, HCILEEncrypt, HCILEAddDeviceToWhiteList) now encode through their existing append directly, dropping the redundant Foundation wrappers.
• import Foundation removed from 167 of 172 files. The remaining five (BluetoothHostController, HCILESetScanEnable, HCIError, HCIPacketHeader, HCICommandTimeout) genuinely use Foundation.Data/TimeInterval/CustomNSError in the host-controller runtime and are left for a follow-up.
• HCIWriteLocalName encodes UTF-8 + zero padding without constructing intermediate Foundation.Data; the crashing HCISetEventFilter stub keeps its fatalError but under the new signature (implementing it is tracked separately).

Not in scope

Making the host-controller runtime (deviceRequest/receive, garbageResponse(Data)) generic over DataContainer — that is a deeper refactor of the async I/O surface.

Reviewer notes

• Source-breaking: command parameters and packet headers no longer expose .data — use Data(parameter) instead (the test target bridges this internally).
• Encoder bodies were transformed mechanically (return Data([…]) → data += […], builder pattern → direct appends); byte order and field order are unchanged.
• All 279 tests pass in debug and the module lints clean (swift format lint, swiftlint).