feat(usb_device_uac): add I2S example and volume dB callback (AEGHB-1254)

[cgreening]

Description

This PR enhances the USB Device UAC component with better volume control support and adds a new example demonstrating I2S audio integration.

Closes: #586

Component Changes

Added a new set_volume_db_cb callback to the uac_device_config_t structure that provides volume changes in decibels (dB), complementing the existing percentage-based set_volume_cb. This allows applications to implement more accurate gain control using logarithmic scaling.

New Example: usb_uac_i2s

Added a comprehensive example (examples/usb/device/usb_uac_i2s) demonstrating USB Audio Class integration with I2S peripherals:

Features:

• I2S PDM RX for microphone input (mono, 16-bit)
• I2S standard TX for speaker/amplifier output (mono, 16-bit)
• Volume control with dB-to-gain conversion using power-of-10 formula
• Mute functionality with zero-sample output
• Sample clipping to prevent overflow (-32768 to 32767 range)
• Configurable GPIO pins via menuconfig
• Optional amplifier shutdown control (SD_MODE pin)

Hardware Support:

• ESP32-S3 (primary target)
• Works with any I2S PDM microphone
• Works with any I2S PCM amplifier

Documentation Updates

Updated both English and Chinese documentation (docs/en/usb/usb_device/usb_device_uac.rst and docs/zh_CN/usb/usb_device/usb_device_uac.rst) with:

• Usage example of the new set_volume_db_cb callback
• Aligned code formatting in example snippets

Related

• Component documentation: USB Device UAC
• Related to existing usb_uac example but demonstrates I2S peripheral integration

Testing

• ✅ Built successfully for ESP32-S3 target
• ✅ Tested with I2S PDM microphone and I2S PCM amplifier hardware.- NOTE crackly output behaviour requires investigation
• ✅ Verified volume control functionality (both mute and gain adjustment)
• ✅ Tested audio input (microphone) and output (speaker) data paths
• ✅ Confirmed device enumeration on host computer as USB audio device
• ✅ Documentation builds without errors

Test Environment:

• ESP32-S3 development board
• I2S PDM microphone
• I2S PCM amplifier/speaker
• Host: macOS/Windows/Linux (USB audio device recognized)

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Warnings

⚠️

Some issues found for the commit messages in this PR: the commit message "Adds missing callback copy": summary looks empty type/action looks empty Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).

👋 Hello cgreening, we appreciate your contribution to this project!

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[YanKE01]

Hi, @cgreening . I'm really sorry for getting to this PR so late. I was wondering if the example part could be moved to the examples/usb/device/usb_uac routine. We can use kconfig to choose between using the default volume_cb or db_cb. Since the usb_uac routine is based on our development board, this will help standardize the hardware environment for everyone. Additionally, remember to update the version number in the component's idf_component.yml to 1.3.0 and document the changes in the changelog.