test(slowsam): samcli test speed up

[Hweinstock]

Problem

• The test failure is due to timeout on Windows when first searching for the SAM cli path in src/shared/sam/cli/samCliLocator.ts. This is a known slow process.
• The verification of SAM is also slow (100-200ms), even if result is cached and we do this each time we read from cache.

Solution

• Verify the cache once, rather than on each read.
• Find sam cli in the before hook to allow all sam tests to run under same conditions. Otherwise, the first test is then responsible for actually finding the path causing it to take way longer than the rest of the tests.
• Allow 3x retries on before hook on windows to avoid flakiness.

Notes

• An alternative solution could involve manually inserting into the cache, or mocking a piece of the component, but wanted to keep the test coverage as is.
• This approach also allows us to isolate the finding code into its own test (rather than whatever the first test is) to see if there are performance regressions.
• Additionally, retry mechanism was more effective than increasing the timeout in reducing flakiness.

fix #2675

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License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[hayemaxi]

Avoid importing from index.ts files in core, it can cause circular dependencies (e.g. we export this file through that index.ts directly or indirectly). Instead import directly from the file.

[Hweinstock]

Out of curiosity, what purpose does index.js serve if its not supposed to be imported from? Is it just for exporting to external modules?

[justinmk3]

Is it just for exporting to external modules?

Yes, it's for the packages/amazon/ and packages/toolkit/ modules, which depend on packages/core/.