Boost: Fix cache bypass patterns not applied from start of URL

[dilirity]

@donnchawp raised a good point today. If you want to only exclude the page /test from the caching, according to the docs, you would do the following:

For instance, to exclude a shop page from being cached, simply input “/shop” (without the quotes). Place each path on its own line. If you need to exclude multiple pages under a single directory, you can use the wildcard symbol (.*) in your path. This might look like /blog/(.*) to exclude all pages under the “blog” section. 

However, if you do this, you will also exclude anything that contains /test in the url. So for example, you would prevent this URL from being cached: /2025/01/01/test/. This is because the current implementation of bypass pattern matching in Boost is very loose.

Proposed changes:

• Make bypass pattern matching stricter to avoid disabling cache unintentionally;
• Fix possible duplicates in bypass patterns list.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

p1736763366014999-slack-C016BBAFHHS

Does this pull request change what data or activity we track or use?

n/a

Testing instructions:

• Make sure you're using pretty permalinks for both tests.
• Note, that if a page/post is excluded from cache, it doesn't have the cache header x-jetpack-boost-cache present. Only cacheable posts/pages have it (with a value of either miss or hit).

Test that exclusions don't behave as expected (old behavior)

• Make sure you're using Boost 3.7.0 (or trunk) when testing this;
• Add a page with the slug test so the url contains /test;
• Now add a post with the slug test so the url ends with /test;
• Enable cache and make sure that both post and page are cached;
• Add /test to the cache exclusion list;
• The page should no longer be cached. However, if you check the post, it is also not cached.

Test that there can be duplicates in the cache exclusions

• If you have /test in the list, add the full URL of the page after it and save;
• You should end up with /test twice in the list.

Test that exclusions are handled properly (strict matching, new behavior)

• Apply this PR;
• Check the page - it should not be cached;
• Check the post - it should be cached.

Test that there are no duplicates in the cache exclusions

• Make sure you have /test in the list and that the list is saved;
• Add the full URL of the page to it and save the list;
• There should be only one reference to /test in the list.

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[haqadn]

Looks good!