Use subarray instead of the deprecated Buffer#slice

[tylerturdenpants]

Buffer.prototype.slice is deprecated in favour of subarray, and this repo uses it in six places. From @types/node:

/** @deprecated Use `subarray` instead. */
slice(start?: number, end?: number): Buffer<ArrayBuffer>;

It got deprecated because it does not behave like the Uint8Array.prototype.slice it shadows. The Buffer one returns a view over the same memory, the TypedArray one copies. subarray is the honest name for the view, and a view is what all six call sites want, since every one of them immediately calls .toString() on the result.

No behaviour change. Both return a view over the same memory and produce identical output, so this is a rename at the call site:

const a = Buffer.from("hello world");
a.slice(2, 7).equals(a.subarray(2, 7)); // true

The two result.slice(...) calls in Transformer#toString are untouched. Those are String.prototype.slice, which is not deprecated.

tsc was already flagging every one of these, though as a suggestion rather than an error, so pnpm lint was passing and it was easy to miss. Came up in review on #33, and it does not belong in a BOM fix, so it is here on its own.

pnpm test is 70 green. pnpm lint passes lint:types, lint:package and lint:published-types.