[@types/better-sqlite3] Allow statement output to be generic (instead of as unknown)

[beenotung]

Currently we need to cast the result type, or to parse it with static-typed parser. I suggest we allow explictly stating the result type via generic type.

Ideally, the result type could be inferred from the sql string, which may be implemented in the future version.

Current version:

    interface Statement<BindParameters extends unknown[]> {
        /* other fields omitted */
        get(...params: BindParameters): unknown;
        all(...params: BindParameters): unknown[];
        iterate(...params: BindParameters): IterableIterator<unknown>;
    }

Suggested version:

    interface Statement<BindParameters extends unknown[], Result = unknown> {
        /* other fields omitted */
        get(...params: BindParameters): Result | undefined;
        all(...params: BindParameters): Result[];
        iterate(...params: BindParameters): IterableIterator<Result>;
    }

[typescript-bot]

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Pinging the DT module owners: @Morfent, @matrumz, @sant123, @Loghorn, @andykais, @mrkstwrt, @stamerf.

[beenotung]

The generic type can be passed from the prepare method as well

[beenotung]

created pull request in #69359