playTone: short tones were silent, long ones lost their end

[p1oner15]

Proposed Changes

Short tones from playTone() are not heard at all, and longer ones lose their end.

AudioOutputI2S::begin() fills the DMA with silence, and AudioGeneratorWAV stops the output as soon as the last sample is queued, so whatever is still in the DMA never plays. With the default 5 x 576 frames that is 360 ms at the 8 kHz tone rate: tones up to ~360 ms are silent and longer ones are cut by 360 ms. Every blocking call also waits ~70 ms for the first DMA slot.

Changes in src/modules/others/audio.cpp:

• tones use a small DMA, 3 x 80 frames (30 ms at 8 kHz);
• the generated wave gets one DMA worth of silence at the end, so the part that gets cut is silence.

Other audio (WAV/MP3 files, RTTTL, TTS) keeps the default DMA size.

Types of Changes

Bugfix

Verification

audio.tone() from a JS script on the T-Embed CC1101 speaker:

• 30 ms and 150 ms tones: silent before, audible after; 660 Hz read as E5 on a phone tuner (with the frequency fix applied);
• a blocking audio.tone(880, 10) took ~90 ms before and ~45 ms after (now() around the call).

Testing

Tested on LilyGO T-Embed CC1101 Plus (lilygo-t-embed-cc1101). Not tested on other I2S speaker boards.

Linked Issues

None found.

User-Facing Change

Short speaker beeps (menu clicks, JS audio.tone) are audible now; longer tones no longer lose their last ~360 ms.

Further Comments

Opened together with two other tone fixes (wrong pitch, JS non-blocking flag). The three touch playTone() in different places and each applies to dev on its own.