feat: add get_available_sample_rates and get_device_transport_type helpers

[afonsojramos]

Summary

Adds two new helper functions to macos_helpers:

• get_available_sample_rates(device_id) — queries kAudioDevicePropertyAvailableNominalSampleRates and returns the supported sample rate ranges as Vec<AudioValueRange>. For devices with discrete rates, mMinimum == mMaximum; for continuous ranges, they differ.

• get_device_transport_type(device_id) — queries kAudioDevicePropertyTransportType and returns the transport type constant (kAudioDeviceTransportTypeUSB, kAudioDeviceTransportTypeBuiltIn, etc.).

Motivation

These are commonly needed when building audio applications that probe device capabilities — for example:

• Implementing automatic sample rate switching (matching track sample rate to device)
• Distinguishing USB DACs from built-in speakers or Bluetooth devices (to conditionally enable exclusive/hog mode)
• Displaying device capabilities in a settings UI

The sample rate ranges are already queried internally by set_device_sample_rate, but aren't exposed as a standalone function. The transport type property has no existing wrapper.

Both functions follow the same patterns as the existing helpers (get_device_name, get_hogging_pid, etc.).

Test plan

• test_get_available_sample_rates — verifies the default output device returns at least one rate range with valid min/max values
• test_get_device_transport_type — verifies the default output device returns a transport type without error
• All existing tests continue to pass

[simlay]

Could you minimize how much is in the unsafe blocks and throw in a // SAFETY comment on them? I'm sure a lot of this repo doesn't have great examples of this in the past - I think this repo predates folks throwing in safety comments.

[afonsojramos]

@simlay Fair, just refactored 👍

[simlay]

LGTM. I checked out your branch, and noticed all the other unsafe blocks in the file that are quite similar to your original. Thanks for upping the quality of comments!

There was a minor nit I had so I pushed a change to your branch. Weirdly enough, that change also fixed clippy and I'm confused why.

Anyway, want me to publish a 0.14.1 release so you can use these features from crate.io?

[afonsojramos]

Thanks for the quick review @simlay! I think that moving the ? outside the unsafe block is cleaner and it likely fixed clippy because the early-return path from ? isn’t itself unsafe, so having it inside the block was the trigger for the lint about unnecessary unsafe scope.

And yes, a 0.14.1 release would be great, would love to use these from crates.io! 🙏

[simlay]

Released via #150.