(future) Consider ReadOnlySequence everywhere

[Warpten]

(ReadOnly)Span<T> is limited to int.MaxValue amout of entries. For all intents and purposes this is fine but is bound to break on files larger than 2GB. The alternative here is to instead use (ReadOnly)Sequence<T>, but this introduces the need for special care across individual span boundaries.

Normally this is also a non-issue because TACT || CASC files are not larger than 2 GB, but this is something to keep in mind for the future.

The general consensus would be to use ReadOnlySequenceAccessor and work off the sequence, trying to abstract away the span boundaries.

References:

1. Memory<T> and large memory mapped files dotnet/runtime#24805