fix: handle sliced Buffer byte ranges in ECDH/DH native bridge

[tp26610]

Summary

This PR fixes ECDH/Diffie-Hellman behavior when input keys are provided as Buffer views (non-zero byteOffset), which previously could pass an incorrect memory range to the native bridge.

What changed

• Add regression test for ECDH computeSecret() using a sliced public-key Buffer in the RN example test suite.
• Ensure ECDH and Diffie-Hellman bridge calls convert Buffer inputs using the exact [byteOffset, byteOffset + byteLength) range before passing to native.

Why

Node-compatible crypto APIs should treat Buffer views correctly.
Without exact-range conversion, sliced Buffers may expose extra bytes from the underlying ArrayBuffer and cause invalid key parsing or mismatched shared secrets.

Test plan

• Added regression test: ECDH computeSecret with sliced public key Buffer
• Existing ECDH tests continue to pass in RN example test suite
• Verify Android example app build still succeeds