harden bounds checks and layout size validation in providers

[jmestwa-coder]

slotmem: harden bounds checks and layout size validation in providers

• Add overflow-safe calculations for slot layout sizes to prevent under-allocation from integer wraparound.
• Validate slot id before pointer arithmetic to avoid undefined behavior.
• Enforce bounds on get/put so copy lengths cannot exceed slot size, and reject invalid buffers.
• Fix out-of-bounds read in release-path logging when id is out of range.
• Validate shared-memory segment size during attach before deriving internal pointers.
• Apply these checks consistently across both shared-memory and plain slotmem providers.

These changes ensure slotmem operations stay within defined memory boundaries and handle invalid inputs safely, while preserving all valid existing behaviour.