Fix ctimer PWM 0% duty cycle behavior

[jerrysxie]

• The length channel match register was off by one, causing 0 duty cycle pwm to have 1 tick of high output instead of always low.

• Add example test for 0% and 100% duty cycle behavior using GPIO input monitoring.

closes #539

[Copilot]

Pull request overview

This pull request fixes an off-by-one error in the CTimer PWM period configuration that caused 0% duty cycle PWM to output one tick of high signal instead of staying always low. The fix adjusts the period match register value to account for zero-based counting.

Key changes:

• Fixed period calculation in CTimerPwmPeriodChannel::new() by subtracting 1 from period_clock_ticks to properly handle zero-based timer counting
• Added PIO0_30 pin support for CTimer match output
• Added example test demonstrating correct 0% and 100% duty cycle behavior using GPIO monitoring

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
src/timer.rs	Fixed off-by-one error in PWM period configuration by subtracting 1 from period_clock_ticks; added PIO0_30 pin support
examples/rt685s-evk/src/bin/ctimer-pwm-0-100.rs	New example testing 0% and 100% duty cycle behavior with GPIO input monitoring

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/timer.rs:1063

• There's an inconsistency between the value written to the hardware register and the value stored in count_max. Line 1057 writes period_clock_ticks - 1 to the hardware (which is correct for the fix), but line 1063 stores the unadjusted period_clock_ticks in count_max. This inconsistency will cause incorrect duty cycle calculations in set_duty and get_duty functions since they use count_max as the scale factor. The count_max should be set to period_clock_ticks - 1 to match what was written to the hardware register.

        channel_info.pwm_configure(period_clock_ticks - 1);

        Ok(Self {
            _lifetime: PhantomData,
            period,
            clk_freq: clock_rate,
            count_max: period_clock_ticks,

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