Allow user to control lifetime of Buffer object

@nselliott is already working on this.

Since Dec 9, 2024.

Many Sidre users will never interact with *Buffer* objects directly. They are created as part of creating a *View* and released when there are no *Views* associated with the *Buffer*.

However, there are cases where the user cares about the lifetime of the *Buffer*. For example, they create a *Buffer* with ``createBuffer`` then create several *Views* which use consecutive blocks in the *Buffer*. When the *Views* are destroyed the user has no convenient way to preserve the *Buffer*.

A field should be added to the *Buffer* object to define ownership. When ``createBuffer`` is called by the user, ownership is set to the user. Calls to ``createBuffer`` internal to the library should set ownership to the library. Then when the last *View* is removed from a *Buffer* the *View* will no longer be deallocated if the user owns the *Buffer*.

If the *Buffer* is created by the library, then extracted by the user via ``getBuffer`` and used to create another *View*, the old semantics should still apply. This keeps the ownership model simple since only ``createBuffer`` defines user ownership.

Issue #674 should include a flag to force destruction of user owned *Buffers*.

When the DataStore destructor is called, all *Buffers* should continue to be destroyed.