Revert `MemorySegmentManager::memory` field visibility

[gabrielbosio]

MemorySegmentManager::memory was changed to public in v2.0.1. This change of visibility was not necessary and it was a mistake.

Next releases (for both 2.x.y and 3.x.y) should revert MemorySegmentManager::memory visibility back to pub(crate). This will disable access of public functions implemented in Memory after making MemorySegmentManager::memory public. Next releases should include functions to keep access of the logic the mentioned public functions would not provide by reverting back the field visibility.

For example, see this function from vm/vm_memory/memory.rs:

pub fn get_maybe_relocatable(&self, key: Relocatable) -> Result<MaybeRelocatable, MemoryError> {
  // ...
}

There should be a function in vm/vm_memory/memory_segments.rs that calls the function mentioned above:

impl MemorySegmentManager {
  // ...
  pub fn get_maybe_relocatable(&self, key: Relocatable) -> Result<MaybeRelocatable, MemoryError> {
    self.memory.get_maybe_relocatable(key)
  }
  // ...
}

[gabrielbosio]

Hi, @enitrat, just letting you know we will address this issue soon.

Because MemorySegmentManager::memory field will no longer be public, the function Memory::get_maybe_relocatable you added in #2039 won't be accessible from MemorySegmentManager. These changes will be included in next releases from both 2.x.y and 3.x.y.

[gabrielbosio]

@enitrat we will revert this change in #2176 so MemorySegmentManager::memory will be kept public