Refactor: introduce lookahead() in DecompressionPlanner

[Rolf-Smit]

Renamed isCalculatingTts to isLookahead and resetAfter() to lookahead(). The lookahead method now manages the isLookahead flag itself, so all calculations that previously used resetAfter() (TTS, find-ceiling and ceiling-cleared checks) no longer emit per-minute intermediate segments.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.77%. Comparing base (27b7731) to head (1b8b27e).

Files with missing lines	Patch %	Lines
...ysner/domain/decompression/DecompressionPlanner.kt	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #171      +/-   ##
==========================================
- Coverage   69.80%   69.77%   -0.04%     
==========================================
  Files         141      141              
  Lines        7578     7576       -2     
  Branches      933      933              
==========================================
- Hits         5290     5286       -4     
- Misses       1810     1813       +3     
+ Partials      478      477       -1     

Flag	Coverage Δ
domain	77.67% <91.66%> (-0.17%)	⬇️
presentation	67.82% <ø> (ø)

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