feat(erc2535): Diamonds multi-facet proxy with loupe and tests

[jose-compu]

Description:

Implements EIP-2535 Diamonds: a single proxy contract that delegates to multiple facet contracts via a selector→facet mapping.

• Interfaces: IDiamond (FacetCut, DiamondCut event), IDiamondCut (diamondCut), IDiamondLoupe (facets, facetFunctionSelectors, facetAddresses, facetAddress).
• LibDiamond: ERC-7201 namespaced storage, add/replace/remove facets, only-owner checks, init delegatecall. Custom errors for invalid cuts and init revert.
• Diamond.sol: Proxy with immutable loupe + diamondCut (no storage for those selectors); fallback delegatecall; _rejectImmutableRemoval blocks removal of loupe/cut selectors.
• Tests: 19 tests (loupe, add/replace/remove, only-owner, duplicate selector, replace selector-not-found, remove immutable revert, constructor with initial facets, receive ETH, diamondCut with init, fuzz for setValue/getValue and add).

ROADMAP and README updated for ERC-2535.