docs: Std docs

What I think would be useful to include:

• info about JS and STD operators (add, sub, mul, div):
  • JS doesn't have operator overloading (yet), so we need extra functions for vectors and matrices,
  • our casts mimic WGSL casts, but still return numbers, so d.u32(1)/d.u32(2) is still 0.5,
  • (if #1022 is closed) the possibility of using infix notation,
• we implement some of WGSL standard library, including arithmetic, atomic, synchronisation, packing and texture sampling operations (it probably is unnecessary to list all of the functions, a link to this file should be enough until we have auto-generated docs),
• we provide TGSL implementations of some wgpu-matrix functions,
• we provide some extra utilities like isCloseTo, allEq.

Start by reviewing packages/typegpu/src/std/index.ts, which the issue identifies as the current standard-library reference. Use the issue’s list of operators, WGSL-related functions, wgpu-matrix functions, and utilities to determine the documentation sections needed; done means these capabilities are described with an appropriate link until auto-generated docs exist.