Long-term: remove the const_cast workaround in SLEBase's resolveEntry()

[mvadari]

SLEBase's resolveEntry() helper (include/xrpl/ledger/helpers/SLEBase.h) uses const_cast<ReadView*> to reach ApplyView::peek() from a ReadView const&. This is safe today only because xrpld never holds a truly const-qualified ReadView, but it's fragile.

Ideas raised in PR #7886 review, roughly in order of preference:

1. Fix ApplyView::read() to use the cache (see ApplyView::read() doesn't go through the apply-state-table cache like peek() does #8068) — would remove the need for this workaround entirely.
2. Add a const peek() to ReadView that just calls read(), and call peek() here unconditionally.
3. Make ApplyView::peek() a const function (with the members it touches mutable), then cast view to ApplyView const* instead of stripping const off a ReadView*.