feat: add getTimeline() and refactor data compression

[tonypconway]

This PR does three things:

• feat: Adds a new getTimeline() method for getting the series of minimum browser changes, either grouped by date or by browser.
• refactor: Substantial refactoring of the data compression process that replaces the full list of browsers from @mdn/browser-compat-data and downstream-browsers.json and features from web-features (in their very pared down form) with a change-list timeline that reflects which versions supported Baseline (newly available) on a given date. Thanks to @swwind for the idea!
• refactor: Some common functions have been moved to a util.ts module for use in other scripts.
• fix: Removes process.exit() calls when unsupported option combinations are passed to getCompatibleVersions() and getAllVersions() in favour of throwing an Error. There is a small security risk with process.exit() calls that sites accepting unsanitised inputs could be the subject of attacks. Unsupported config options now throw and Error which should allow for more graceful handling. Thanks to @bnbdr for flagging this as vulnerability CVE-2026-45819 .

Fixes #134

[swwind]

Besides, why do I have the permission to click the "Approve" button for this PR? It doesn't look like I have the write permission to this repo or something else.

[tonypconway]

I think because my initial branch was base on yours, GitHub automatically made you a read-only approver.

I'm pretty comfortable with where this has landed.

FYI @ai , I have made some architectural changes to this module to support your friends working on browserslist-rs and improve performance. I've tested against browserlist and this is reliably giving the same output as before, so I'm going to push live on Wednesday if I don't hear any objections. Cheers!

[swwind]

I think because my initial branch was base on yours, GitHub automatically made you a read-only approver.

In fact, I've found that anyone can submit an white "approve" decision for any pull request in any project. Perhaps this is a feature of GitHub. I hope I haven't messed up this PR.

[tonypconway]

Ah right, just good vibes then, haha. You can set rules around PRs needing approvals before the can be merged, but that's not needed her, just needs to pass the test matrix. Then one of the web-platform-dx owners or I can merge it (I'll squash the commits before merging for cleanliness).

[swwind]

@tonypconway Just a gentle ping here, is there any remaining issues before this can be merged? Happy to help if needed.

[tonypconway]

So sorry, have had some family commitments and sickness blocking me for the last few days. Merging and publishing as v2.11.0 now. For some reasons one of the CLI tests timed out on certain Node versions, but it seems to be environmental rather than a problem with the package, as a re-run of the tests was successful: https://github.com/web-platform-dx/baseline-browser-mapping/actions/runs/29837636545