add "esmock.strictest"

This release adds esmock.strictest --a stricter version of esmock.strict which requires every module imported to the target module to be mocked,

• add support for esmock.strictest, a more-strict variant of esmock, per @gmahomarf
• use more-descriptive internal-variable "treeId", rather than "esmockKey"
• include .mjs files in eslint filter and lint-fix existing .mjs files