Resolve rustfmt/changelog CI failures in STM32F469 Disco display-touch updates

[Copilot]

The PR fixes the formatting regressions reported by the rustfmt job (including macro-call layout and assignment handling in touch error throttling paths) and adds the missing changelog update required by changelog-enforcer.

• Rustfmt conformance in touch polling paths

  • Normalized defmt::warn! call formatting in examples/f469disco-lcd-test.rs to rustfmt-accepted form.
  • Kept explicit counter mutation semantics in retry/error-throttle code paths while aligning with formatter output.

• Whitespace/format cleanup in example module

  • Removed formatting-only drift in examples/f469disco/nt35510.rs (trailing-space delta picked up by rustfmt).

• Changelog gate fix

  • Added an Unreleased entry in CHANGELOG.md summarizing the PR scope (STM32F469 Disco display/touch example improvements and dma module exposure).

// before (non-rustfmt form in failing diff)
defmt::warn!(
    "detect_touch read error (attempt {})",
    attempt + 1
);

// after
defmt::warn!("detect_touch read error (attempt {})", attempt + 1);

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