Make `SigSpecConstIterator` work with packed `SigSpec`s and use it instead of `SigSpec::operator[] const` in some places#5415

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rocallahan wants to merge 8 commits intoYosysHQ:mainfrom

rocallahan:sigspec-const

Commits on Oct 24, 2025

Add SigChunk::offset_in_sigspec
rocallahan
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Make `SigSpecConstIterator` iterate over SigSpec without unpacking
rocallahan
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Avoid unnecessary copying when applying a SigMap to a SigSpec
rocallahan
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Make SigSpec::lsb()/msb() use SigSpecConstIterator instead of indexing
rocallahan
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Replace use of `SigSpec::operator[] const` in sigtools with iterators
rocallahan
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Make `FfInitVals` use `SigSpecConstIterator` instead of `SigSpec::operator[] const`
rocallahan
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Make modtools use `SigSpecConstIterator` instead of `SigSpec::operator[] const`
rocallahan
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Make rtlil.cc use `SigSpecConstIterator` instead of `SigSpec::operator[] const`
rocallahan
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