Migrate from BitMaskOptionSet to native OptionSet

[colemancda]

Summary

Replaces the deprecated BitMaskOptionSet / BitMaskOption (both marked @available(*, deprecated, message: "Use OptionSet instead") in the Bluetooth package) with native Swift OptionSet structs. This clears every BitMaskOptionSet is deprecated warning in the build.

Each flag enum + BitMaskOptionSet<Flag> pair becomes a single OptionSet struct, keeping the original type name so public API and the DocC references stay intact — the same idiom the Bluetooth package uses for its own flag types (e.g. CTEType).

Type	Before	After
RFCOMMFlag	enum: BitMaskOption	struct: OptionSet (UInt32)
RFCOMMLinkMode	enum: BitMaskOption	struct: OptionSet (UInt16)
HCIDeviceFlag	enum: BitMaskOption (bit positions)	struct: OptionSet (UInt32, 1<<n masks)
HostController.ScanOption	enum: BitMaskOption	struct: OptionSet (UInt16)

HCIDeviceOptions.flags / contains were rewritten to OptionSet semantics (intersection(.all) / isSuperset(of:)). This also fixes a latent bug: the old BitMaskOptionSet<HCIDeviceFlag> could not represent .up (bit position 0 collapsed to "empty"), so options.flags silently dropped it — the native OptionSet masks (1<<n) represent it correctly.

Verification

• Debug build: clean, zero BitMaskOptionSet deprecation warnings
• Debug tests: all pass
• Release (library) build: passes

Base branch

Targets feature/code-coverage rather than master: this branch was cut from it and depends on that branch's Bluetooth-master API fixes (.data → Data(_:), updated UUID namespaces) to build against the current Bluetooth dependency. It will retarget to master automatically once #52 merges.