Release 4.4.1 - Minor refactoring and update

Overview

Minor quality-of-life release for audio output, especially PWMAudio. Precalculating values turns a 65K soft-FPU operation into a linear search of 12 entries in 99.9% of the cases.

I2S and PWMAudio and BluetoothAudio now share a common audio interface to simplify code like BackgroundAudio or ESP8266Audio.

Audio-related

• Allow setting PWMAudio frequency before begin (#2726)
• Properly wrap AudioBufferManager block writes (#2725)
• Add AudioOutputBase keyword
• Precalculate common PWMAudio dividers, avoid noise (#2714)
• Add real block write for AudioRequestBuffer (#2712)
• Overclock to 153.6 MHz (instead of 147.6 MHz) for I²S 48 kHz sample rate (#2708)

Infrastructure

• Use the distributed ARM ar in libpico, not system (#2721)
• Don't go through runtime initializers when there is no OTA command (#2697)
• Fix issue with undefined LED_BUILTIN on Seeed Xiao RP2350 (#2704)