feat(thegraph-core): add fake_impl module and alloy fake support

[LNSD]

This pull request introduces a new module for generating random test data using the fake crate and updates existing code to utilize this new module.

New module for generating random test data:

• thegraph-core/src/fake_impl.rs: Added a new alloy module for implementing the fake crate traits.
• thegraph-core/src/fake_impl/alloy.rs: Implemented the fake crate for generating random test data for various alloy crate types, including Address, B256, PrimitiveSignature, and U256.

Updates to existing code:

• thegraph-core/src/allocation_id.rs: Modified the dummy_with_rng implementation for AllocationId to use the new Alloy struct.
• thegraph-core/src/indexer_id.rs: Modified the dummy_with_rng implementation for IndexerId to use the new Alloy struct.
• thegraph-core/src/lib.rs: Added the new fake_impl module under a feature flag.