[KMP] Fix memory leak found in PublicKey

[10gic]

Description

Fix issue #4096

How to test

Types of changes

Checklist

• Create pull request as draft initially, unless its complete.
• Add tests to cover changes as needed.
• Update documentation as needed.
• If there is a related Issue, mention it in the description.

If you're adding a new blockchain

• I have read the guidelines for adding a new blockchain.

[10gic]

Before fixing:

After fixing:

Test case:

println("Test started")
val publicKeyHex =
    @Suppress("ktlint:standard:max-line-length")
    "044ba28b11af1561042b03b9d0f940446315af11358aa12d798050b3cf76265dab0f48b22ea1fc1f9560c969b966221f2821b746c4e56efaeaeec8689caf5843c9"
var i = 1
val publicKeyByteArray = publicKeyHex.hexToByteArray()
while (i <= 10_000_000) {
    val publicKey = PublicKey(publicKeyByteArray, PublicKeyType.SECP256k1Extended)
    if (i % 20_000 == 0) {
        println("Test case $i run")
    }
    i++
}
println("Test completed")

[satoshiotomakan]

LGTM, big thanks for the finding!