Extract hardcoded delay values into named constants

[coderabbitai]

Context

In PR #105, there's a hardcoded delay value of 50_000 microseconds (50ms) in the chip_reset method:

self.chip.delay_us(50_000); // 50 msec delay

Task

Extract this and other hardcoded delay values into named constants to make them more prominent. This is part of an eventual goal to remove delays if possible.

References

• PR: Support to boot into download mode. #105
• Comment: Support to boot into download mode. #105 (comment)
• File: winc-rs/src/manager.rs:264

Acceptance Criteria

• Replace hardcoded delay values with named constants
• Constants should have descriptive names indicating their purpose
• Consider grouping related delay constants together