Add limited size memory cache backend

[lucasmrdt]

What do these changes do?

Adds a new LimitedSizeMemoryCache backend that extends SimpleMemoryCache with LRU (Least Recently Used) eviction policy and configurable size limits. The cache automatically evicts least recently used items when the size limit is exceeded.

Are there changes in behavior for the user?

Yes, users now have access to a memory-constrained cache backend. The new cache:

• Accepts a max_size_mb parameter (default: 64MB) to limit total cache size
• Uses LRU eviction when the size limit is reached
• Optionally raises MemoryError when trying to cache items larger than the limit (via raise_on_oversize=True)
• Is available as aiocache.LimitedSizeMemoryCache and included in the default cache backends list

Related issue number

None

Checklist

• I think the code is well written
• Unit tests for the changes exist (in tests/ut/backends/test_limited_memory.py)
• Documentation reflects the changes (in docs/caches.rst)

[Dreamsorcerer]

This seems too close to #1027. I think anything more complex should be done in an external library and linked from the docs.