WASM: defer eager Numba gufunc/jit compilation to first use (#930)

[kp992]

Closes #930, part of #925.

What

Four guvectorize callables compiled at import quantecon time are now compiled lazily on first call:

Callable	File	Change
_probvec_parallel	random/utilities.py	module-level gufunc → lazy Python wrapper
_probvec_cpu	random/utilities.py	same
_sample_without_replacement	random/utilities.py	@guvectorize decorator → lazy wrapper
_ints_arr_to_bits	game_theory/vertex_enumeration.py	same

How

Gufuncs are replaced by thin Python wrapper functions that create the underlying ufunc on first call and cache it in a module-level sentinel. _probvec_cpu keeps the same name so the game_theory/random.py import is unchanged.

Why this matters for WASM

On native CPython, eager compilation costs milliseconds. In a JupyterLite/WASM kernel, each compile is a full LLVM optimise + WASM object emit + in-process LLD link. The emscripten-forge Numba patches also force-disable cache=True for @guvectorize, so the four gufunc compiles were paid on every session on the critical import path of every notebook.

Public API

No change. qe.random.probvec(..., parallel=...), qe.random.sample_without_replacement(...), and qe.game_theory.vertex_enumeration(...) are unaffected.

[coveralls]

coverage: 90.786% (+0.006%) from 90.78% — kp992:wasm-930-lazy-numba into QuantEcon:main

[mmcky]

Thanks @kp992. Now that #938 is merged, could you rebase this onto main and drop 97518e0 (the int64 widening from #942)? #929 concluded the intp typing in comb_jit is intentional since its result is an array size, so please keep intp and drop the np.int64 casts, INT64_MAX, the MAX_INT64/test_max_int64 renames and test_simplex_grid_comb_int64 — the lazy @jit(nopython=True, cache=True) over the unchanged body is all #930 needs. The "Depends on #942" line can go too.

Two more things. #930 asks for a before/after warm-cache import quantecon timing in JupyterLite before this merges — could you add it to the PR description, or say so if you can't and we'll decide whether to waive it. And this doesn't address #944 (the upstream reproducer in emscripten-forge/recipes#6309 uses lazy @njit(cache=True) functions only), so please don't reference it as such.