Feature: Add ERC1155 multi-token standard properties

[omarinuwa]

Implements comprehensive property tests for ERC1155 multi-token contracts following EIP-1155. Addresses GitHub issue #57.

Adds 30 properties across 6 files:

• ERC1155BasicProperties (14 properties): Balance tracking, single/batch transfers, operator approvals, and safe transfer receiver checks
• ERC1155BurnableProperties (6 properties): Single and batch burn operations with proper authorization checks
• ERC1155MintableProperties (8 properties): Single and batch mint operations with safe receiver validation

Each property includes:

• Full NatSpec documentation with title, notice, dev notes, and invariants
• Unique property IDs (ERC1155-BALANCE-001, ERC1155-TRANSFER-001, etc.)
• Testing mode indicators (INTERNAL/EXTERNAL)
• Organized sections with descriptive headers

Property Categories:

• Balance Properties: Zero address balance, batch consistency
• Transfer Properties: Zero address protection, balance updates, self-transfers, batch operations, array validation
• Approval Properties: Operator approval management, authorization checks
• Safety Properties: Receiver interface validation for safe transfers
• Burn Properties: Balance reduction, approval requirements, batch operations
• Mint Properties: Balance increases, zero address protection, receiver checks

Both INTERNAL and EXTERNAL testing approaches supported:

• Internal (3 files): Test harness inherits from token implementation
• External (3 files): Tests interact through public interface only

Base contracts and utilities:

• ERC1155TestBase: Base for internal testing with MockReceiver1155
• ERC1155ExternalTestBase: Base for external testing
• MockReceiver1155: Test contract for safe transfer callbacks
• IERC1155Internal: Interface for external testing

[CLAassistant]

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