RFR: 8356706: Foreign tests timeout after passing on linux-x64-zero

[Per Minborg]

This PR improves the robustness of tests on slow machines such as "zero" variants. The timeout was increased to 10 minutes for both tests. There are many combinations in `TestAccessModes`, so the test takes some time even on a fast machine. In `StdLibTest`, there are numerous native calls, and these can be much slower on "zero" machines. In the latter test class, I made some attempts to improve performance. On my M1 machine, the test was about 10% faster with the changes (but I only did one run, so this might be in the error margin).

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Commit messages:
 - Improve robustness of tests on slow machines

Changes: https://git.openjdk.org/jdk/pull/25248/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25248&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356706
  Stats: 32 lines in 2 files changed: 0 ins; 0 del; 32 mod
  Patch: https://git.openjdk.org/jdk/pull/25248.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25248/head:pull/25248

PR: https://git.openjdk.org/jdk/pull/25248