Check account boundaries on overlapping memmove syscall

[seanyoung]

Problem

Since SIMD-0219, any memmove cannot cross account data and non-account data boundaries. This was implemented in PR 3744.

However there was a check missing: memmove may do an overlapping copy which requires reverse iteration, and this code path did not have the check in place.

Summary of Changes

• Add missing check and add tests
• Since v2.1 is already on testnet, this needs a new feature
• Feature can be folded into direct mapping feature in the future
• Rekey direct mapping

Found by @yufeng-jump and @mjain-jump

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.

[mergify]

Backports to the beta branch are to be avoided unless absolutely necessary for fixing bugs, security issues, and perf regressions. Changes intended for backport should be structured such that a minimum effective diff can be committed separately from any refactoring, plumbing, cleanup, etc that are not strictly necessary to achieve the goal. Any of the latter should go only into master and ride the normal stabilization schedule. Exceptions include CI/metrics changes, CLI improvements and documentation updates on a case by case basis.