Rewrite of Chmy.jl

[utkinis]

Description

This PR implements a complete overhaul of Chmy.jl for version v0.2. The new implementation introduces a symbolic layer for representing finite-difference expressions on regular grids, as well as modules for tensor algebra and tensor calculus.

Remaining tasks

The following features still need to be implemented before merging this PR:

• Combined operators encapsulating expressions for both the grid interior and boundaries.
• Grouping expressions for parallel computation based on the memory throughput heuristic.
• Generating KernelAbstractions (KA) kernels for computing expression groups.
• Interpolation operators.
• Coordinates in reference coordinate system.
• Grid recipes: Arakawa staggered grids, MAC grid, FSG.
• Lowering expressions to grid stencils based on a recipe.
• Allocating bindings from lowered expressions.
• First-class support of periodic grids.
• Examples: symbolic layer, diffusion, wave propagation, Stokes, curvilinear grids, hyperbolic equations.
• Docstrings.
• Documentation.
• Fix CI (Chmy.jl v0.2 only works on Julia 1.12+).
• Uniform STensor, which ignores indexing and grid locations during lowering.
• Immediate lowering on indexing.
• Broadcasting over Tensor.