feat(AggLayer): Solidity compatibility tests for MMR frontier code

[mmagician]

As suggested here, we're getting to a stage with the AggLayer integration where we should check for compatibility with the Solidity implementation.

This PR adds a small foundry project inside the miden-agglayer crate:

• forge commands to generate the test vectors. The vectors are generated by calling the Solidity functions of interest _addLeaf & getRoot
• make generate-solidity-test-vectors command to locally re-generate the test files
• Rust test which reads the test vector as a reference, and compares with the Rust implementation KeccakMmrFrontier32 (currently we're not comparing with the output of MASM, since we independently already have Rust<>MASM compatibility test, so by extension we have Solidity<>MASM compat)
• for now, no CI job that re-generates the test vectors. If desirable, we can consider adding this later

To be done in a follow-up PR:

• move miden-testing/agglayer code into miden-agglayer crate. Otherwise, the Rust compat test (located in miden-testing depends on the test vectors which are generated in a different crate (miden-agglayer)

[mmagician]

nit: to be changed once #2313 lands