fix(node): preserve camelCase keys for webhook template args

[johnpmitsch]

Summary

• The Node binding's node_ta_to_core was snake-casing the inner args object before deserializing into core::webhooks::TemplateArgs. Core's EvmContractEventsTemplate carries #[serde(rename_all = "camelCase")] and expects eventHashes, so the snake-cased event_hashes was silently dropped during deserialization. The outbound serializer then omitted the now-None field (skip_serializing_if), and the API rejected the request with HTTP 500: "Expected array for arg eventHashes" — independent of whether the caller actually supplied the field.
• Webhook template inner structs in core are modeled around the API wire format, so they don't need the per-field case conversion that stream destinations require. All other template structs only have single-word fields where camelCase and snake_case coincide, so dropping the conversion is safe across templates.
• Adds a regression test in crates/node/src/webhooks_template.rs covering the evmContractEvents + eventHashes path (deserialize and re-serialize), plus end-to-end coverage of EvmContractEvents in the webhooks_e2e examples for all four languages.
• Documents in CLAUDE.md not to silence clippy::panic/clippy::unreachable in tests by default — prefer assert!(matches!(...)) or let ... else { unreachable!() }.

Test plan

• cargo test -p sdk-node --lib — new regression test passes
• cargo test -p quicknode-sdk --lib — 203 core tests still pass
• just lint — clippy + tests, -D warnings
• cargo fmt --check
• just node-build — Node binding compiles and smoke test runs
• Live API e2e against evm-contract-events (requires QN_API_KEY; manual)