chore(shadertools): strict null checks, satisfies shader module (9.1)

[ibgreen]

For #

Background

• deck.gl has requested that luma.gl implements typescript strictNullChecks options

Change List

• apply strict null checks to shadertools module.
• Refactor shader module objects to use const satisfies to avoid wiping out detailed type information by "assigning" the ShaderModule type to the object. (most of the "strict null" issues were related to shader module definitions so this was not just a better dev exp thing, but a relevant refactor).