feat: Add getRandomBytes

[FrederikBolding]

Explanation

Add utility for generating cryptographically secure random numbers.

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
New additive API with input validation and tests; no changes to existing crypto primitives or consumers.

Overview
Adds getRandomBytes to @metamask/cryptography as a small wrapper around globalThis.crypto.getRandomValues, returning a Uint8Array of the requested size.

The function rejects non-positive lengths with a clear error. It is re-exported from the package entrypoint, covered by unit tests (length, CSPRNG call, zero-length throw), and noted in the package changelog under the initial release notes.

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[Mrtenz]

Maybe validate length > 0?

[FrederikBolding]

Sure!

[FrederikBolding]

6aa9eed