refactor(dma): move DMA_MAX_TRANSFER_SIZE to dma module and init during HAL startup

Address felipebalbi's review comments on PR #52:

- Move DMA_MAX_TRANSFER_SIZE constant from lpuart/mod.rs to dma.rs
  where it logically belongs (describes eDMA4 hardware limitation)
- Add public dma::init() function called during hal::init() instead
  of lazy initialization via ensure_init()
- Remove ensure_init() entirely since it's no longer needed
- Remove ensure_init() calls from DmaChannel::new() and from_token()
- Remove ensure_init() calls from examples (dma_channel_link, dma_scatter_gather)
- Refactor lpuart_ring_buffer example to use LpuartDma::new() + split()
  pattern instead of separate TX/RX drivers
- Add [lints.rust] section to suppress unexpected_cfgs warning for 'rt'
  feature used by embassy_hal_internal::interrupt_mod! macro

This makes DMA initialization explicit during HAL startup (like GPIO)
and keeps DMA-specific constants in the DMA module.

0 files changed, 0 insertions, 0 deletions