Remove dependencies on noble/curves, hashes from @hpke/dhkem-secp256k1.

[dajiaji]

Is your feature request related to a problem? Please describe.

noble/curves and noble/hashes are excellent libraries, but we only require a small subset of their functionality.
Since full-scope version upgrades occur relatively frequently, keeping up with them incurs ongoing maintenance costs. Moreover, dependencies on external libraries can introduce supply chain vulnerabilities.

Describe the solution you'd like

Therefore, we intend to import only the minimal necessary functionality into hpke-js and maintain it internally.

Describe alternatives you've considered

Nothing.

Additional context

Nothing.

[paulmillr]

Is the idea to inline noble-curves into the dhkem itself? Seems like a nice one.

Since full-scope version upgrades occur relatively frequently

v1 => v2 took 2.5 years, to be precise. There were no breaking changes during v1. There are some in v2 but huge effort was made to keep upgrade/docs as smooth as possible.