Potential fix for code scanning alert no. 18: Implicit narrowing conversion in compound assignment

[Avery-Dunn]

Potential fix for https://github.com/AzureAD/microsoft-authentication-library-for-java/security/code-scanning/18

In general, the fix is to ensure that the left-hand side of the compound assignment is at least as wide as the right-hand side expression. Here, the expression interval[1] - interval[0] is of type long, so sum should also be a long to avoid implicit narrowing when doing sum += ....

The best targeted fix is:

• Change the type of sum from int to long.
• Ensure that subsequent uses of sum (specifically in the division sum/list.size()) perform long arithmetic and then rely on Java’s automatic widening when concatenating with the string; no further changes are necessary there because sum being long is acceptable and safe.

Concretely, in msal4j-persistence-extension/src/test/java/com/microsoft/aad/msal4jextensions/CacheLockTestBase.java, inside validateLockUsageIntervals:

• Update line 111 from int sum = 0; to long sum = 0L;.
  No new imports, methods, or definitions are required.

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