PR merge coordination: T=1 USART reconfig (#40) and Half-duplex USART (#41)

[Amperstrand]

Summary

Two open PRs modify overlapping files in the smartcard driver:

• PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40: T=1 USART reconfiguration after ATR (most crucial for SeedKeeper support)
• PR feat(scard): replace skip_bytes echo suppression with explicit half-duplex USART control #41: Half-duplex USART control (replaces skip_bytes echo suppression)

Overlapping Files

• usermods/scard/ports/stm32/scard_io.c
• usermods/scard/ports/stm32/scard_io.h

Recommended Merge Order

Option A: Merge PR #40 only (recommended for now)

• PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40 is most crucial for SeedKeeper support
• Standalone change, no dependencies
• Smaller scope, easier to review

Option B: Merge both PRs

If both are desired:

1. Merge PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40 first (T=1 reconfig)
2. Rebase PR feat(scard): replace skip_bytes echo suppression with explicit half-duplex USART control #41 onto updated master
   • Will need to resolve conflicts in scard_io.c and scard_io.h
   • PR feat(scard): replace skip_bytes echo suppression with explicit half-duplex USART control #41 removes skip_bytes from struct; PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40 doesn't touch it, so rebase should be straightforward

Notes

• PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40 was reviewed and fixed: function declaration is now properly inside include guard
• Both PRs are independent features but touch the same driver files
• PR feat(scard): add T=1 USART reconfiguration after ATR for spec-compliant timing #40 is smaller and has higher priority for SeedKeeper compatibility

cc @Amperstrand