Refactor flash operations to use state-machine approach instead of blocking

[coderabbitai]

Problem

The current flash operations implementation uses blocking operations with long wait times that prevent other firmware operations from running. Specifically:

• FLASH_REG_READ_RETRIES = 10 with FLASH_REG_READ_DELAY_US = 100,000 (100ms each)
• Total potential blocking time: 1 second per operation
• Functions like check_flash_tx_complete() sit in tight loops, preventing other firmware tasks (e.g., LED blinking)

Current Implementation

The flash operations in winc-rs/src/manager.rs use blocking loops in methods like:

• check_flash_tx_complete()
• send_flash_write()
• send_flash_read_status_register()

Proposed Solution

Refactor flash operations to use a state-machine based approach similar to the existing boot_the_chip() function, which allows:

• Non-blocking operation
• Incremental progress tracking
• Other firmware operations to continue running
• Better responsiveness

References

• Original PR: Add support for accessing WINC1500 SPI flash memory #104
• Discussion: Add support for accessing WINC1500 SPI flash memory #104 (comment)

This refactoring would improve firmware responsiveness while maintaining the same flash operation functionality.

[kaidokert]

Further follow-up : one manager.rs code is non-blocking with a state machine, the methods in winc-rs/src/client/flash.rs can become non-blocking too. A future AsyncClient can then also be implemented later.