chore: rename BlockChain to Blockchain

[jsvisa]

I noticed in the code that sometimes it uses Blockchain and sometimes BlockChain. Here are the statistics I gathered:

$ rg Blockchain -c

examples/rpc-db/src/main.rs:3
testing/ef-tests/src/cases/blockchain_test.rs:11
testing/ef-tests/src/models.rs:1
testing/ef-tests/src/suite.rs:2
etc/grafana/dashboards/overview.json:2
testing/ef-tests/tests/tests.rs:2
crates/interfaces/src/blockchain_tree/mod.rs:11
crates/interfaces/src/blockchain_tree/error.rs:18
bin/reth/src/commands/debug_cmd/replay_engine.rs:5
bin/reth/src/commands/debug_cmd/build_block.rs:5
crates/primitives/src/proofs.rs:2
crates/interfaces/src/lib.rs:1
crates/primitives/src/header.rs:3
crates/interfaces/src/error.rs:4
crates/blockchain-tree/src/noop.rs:11
crates/blockchain-tree/src/block_indices.rs:1
crates/blockchain-tree/src/config.rs:4
crates/blockchain-tree/src/blockchain_tree.rs:37
crates/blockchain-tree/src/externals.rs:1
crates/blockchain-tree/src/state.rs:3
crates/blockchain-tree/src/chain.rs:3
crates/blockchain-tree/src/lib.rs:4
crates/blockchain-tree/src/shareable.rs:15
crates/consensus/beacon/src/engine/mod.rs:12
crates/consensus/beacon/src/engine/test_utils.rs:7
crates/node-builder/src/builder.rs:8
crates/net/downloaders/src/bodies/bodies.rs:1
crates/e2e-test-utils/src/lib.rs:2
crates/storage/provider/src/chain.rs:1
crates/storage/provider/src/providers/mod.rs:29
crates/storage/provider/src/traits/state.rs:3
crates/storage/provider/src/traits/tree_viewer.rs:9
crates/storage/provider/src/traits/mod.rs:1

$ rg BlockChain -c
crates/consensus/beacon/src/engine/mod.rs:2
crates/blockchain-tree/src/blockchain_tree.rs:15
crates/blockchain-tree/src/state.rs:9
crates/blockchain-tree/src/block_indices.rs:10
crates/storage/provider/src/test_utils/blocks.rs:3

And I think using Blockchain consistently would be more unified. That's why I submitted this PR.

[mattsse]

I don't really have a preference here

if this doesn't conflict with @rkrasiuk wip lgtm

[rkrasiuk]

fine with me