Update Stats to use atomic operations

[mateeullahmalik]

Issue

The TestHandshakerConcurrentHandshakes test fails with a race condition when testing with maximum concurrent handshakes:

fatal error: concurrent map read and map write
goroutine 559 [running]:
internal/runtime/maps.fatal({...})
github.com/99designs/keyring.(*ArrayKeyring).Get(...)
github.com/cosmos/cosmos-sdk/crypto/keyring.keystore.KeyByAddress(...) 
github.com/LumeraProtocol/lumera/x/lumeraid/securekeyx.(*SecureKeyExchange).getLocalPubKey(...)
github.com/LumeraProtocol/lumera/x/lumeraid/securekeyx.(*SecureKeyExchange).CreateRequest(...)

Changes

• Replaced mutex locks with atomic operations for thread-safe access
• Changed field types from int to int32 to support atomic operations
• Added a GetMaxConcurrentCalls() accessor method for safe value retrieval
• Updated the relevant tests to use the new accessor method

The update preserves the original API contract where Update() still returns a cleanup function that decrements the call count when invoked. These changes should reduce overhead in high-concurrency scenarios.

[Copilot]

Pull Request Overview

This PR addresses a race condition occurring during concurrent ALTS handshake tests by introducing mutex protection in SecureKeyExchange and converting Stats to use atomic primitives for thread safety.

• Introduced atomic operations for call counting and tracking maximum concurrent calls in Stats.
• Updated test assertions to call the new MaxConcurrentCalls() method.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/net/credentials/alts/testutil/testutil.go	Replaced mutex with atomic operations for improved concurrency safety in Stats.
pkg/net/credentials/alts/handshake/handshake_test.go	Updated test assertions to utilize the new MaxConcurrentCalls() method.

[akobrin1]

we can change implementation of Stats to atomic, but we still need Update method to return cleanup function - to correctly analyze that all handshake calls were completed.