test: make timeouts configurable

[johnfinnerty-nz]

Summary

• Add shared default timeouts for normal and long-running tests.
• Allow CI and local runs to override them with TEST_TIMEOUT and TEST_TIMEOUT_LONG.
• Replace the remaining hard-coded Tape timeouts with the shared values.

Closes #407

Testing

• node --check on all six modified JavaScript files
• Smoke check with TEST_TIMEOUT=1234 and TEST_TIMEOUT_LONG=5678
• git diff --check

The repository linter could not run from this checkout path because its clang-format invocation does not quote paths containing spaces. The native LLDB test suite requires a built plugin.