Enter bootloader by double tapping reset button

[zUnixorn]

Applicable Changes

• Feature addition
• Modification to behaviour of existing functionality (potential breaking change)
• Modification to existing public APIs (potential breaking change)
• Bug fix
• User docs modification
• Rust toolchain updates
• Dependency updates
• Workflow change (GitHub Actions)
• Repository housekeeping (e.g. READMEs, licensing, templates, etc.)

Related Issues

#5

Description of Changes

Adds the option to enter the bootloader with a double tap of the reset button. This is useful for entering the RP2040 UF2 bootloader, if the regular boot button is hard to reach.

In the current implementation, the field bootloader_double_tap_reset was added to the keyboard macro. If the bootloader-double-tap-reset feature is enabled, this field can be set and optionally change the default timeout value (200ms).

Like:
#[keyboard(bootloader_double_tap_reset)]
or
#[keyboard(bootloader_double_tap_reset = <val>)]

Testing Instructions

1. Enable the feature in the Cargo.toml and add bootloader_double_tap_reset to the keyboard macro.
2. Compile firmware and flash onto a RP2040.
3. Press the reset button two times in quick succession and check if the UF2 bootloader was entered.

Check-list

• I have updated or added to the user docs where applicable
• I have tested the changes on real hardware if applicable
• The changes do not break compilations with other potentially related feature flags
• Credit given where applicable

[Univa]

Thanks for the PR!

[Univa]

Just a couple more things, then I think this is good to merge.