Correct 'BigInt' types to 'bigint' (and add Typescript checking script)

[jonvuri]

First off, fantastic work on this project! The recent addition of Typescript types is a massive feature, especially for such a complex and unorthodox (in JS) API.

I noticed one small glitch in them when introducing the latest version to my private project, where I had already begun using an older, less comprehensive type declaration and my own bigint types. The glitch is that BigInt types are used, but they should be bigint instead. It's a very confusing situation, but the PascalCased 'object types' for primitive values are actually just the type of the constructor function for the boxed object versions of the primitives. It's usually a mistake to use those as the type of the values themselves, and it can cause issues in usage, the main one being that BigInt and bigint are not assignable to each other (which makes sense, one is a number and one is a constructor function):

Some sources that explain this in some more detail:

• https://stackoverflow.com/questions/76477290/what-is-the-difference-between-bigint-lowercase-and-bigint
• https://typescript-eslint.io/rules/no-wrapper-object-types/

This changeset fixes those types, and it also adds Typescript as a dev dependency, as well as a barebones tsconfig.json and a package.json script to run it and type-check index.d.ts. It wasn't failing before this change, but it's nice to have to make sure type changes don't introduce an internal error.

[sgbeal]

... unorthodox (in JS) API.

For trivia's sake, an explanation of that aspect: non-vanilla JS has never been on our development radar in the upstream project, so the quirks of higher-level tools plays no role whatsoever in its shape. Our high-level APIs (namely the sqlite3.oo1 namespace) provide "a" solution which people can use if they like, while making no claim whatsoever about being "the" solution. We also provide very-close-to-C-native bindings from which more "downstream-idiomatic" solutions can be built, but we leave the creation of those to folks who live in that highly-fluid downstream ecosystem. We'd love to see other solutions evolve, but so far nobody has pulled on that thread.

[tomayac]

LGTM, thank you!

[tomayac]

Released as 3.46.1-build3.