Fix memory leaks in key_to_ECC

[saiashok0981]

Summary

This PR addresses memory leaks in key_to_ECC (located in src/support.cc).

Proposed Changes

• Ensures that all helper BIGNUM allocations (priv_mult, p_pt_x, p_pt_y) and EC_POINT (pt) are freed using BN_free / EC_POINT_free once they are loaded/copied into the main ecc_key.
• Frees BN_CTX (ctx) on all code paths (both success and failure).
• Frees ecc_key (EC_KEY_free(ecc_key)) on failure paths before returning nullptr.
• Uses a unified cleanup label (done:) to ensure no leaks occur regardless of where failure is triggered.