feat: forward integrand args via integrate(..., args=...)

[gomezzz]

What

Lets a parametric integrand be integrated directly, without a lambda wrapper:

def fn(x, alpha, beta):
    return alpha * x[:, 0] + beta

Trapezoid().integrate(fn, dim=1, N=101, integration_domain=[[0, 1]], args=(alpha, beta))

BaseIntegrator.evaluate_integrand already accepted args and called
fn(points, *args), but no public integrate() exposed it. This threads an
args parameter through every integrator — Trapezoid, Simpson, Boole,
GaussLegendre, MonteCarlo and VEGAS.

• args defaults to None (fn(points)), so all existing calls are unchanged.
• Scope is the eager integrate() path; the JIT-compiled path is untouched.

This re-implements the stale PR #188 by Dan Barzilay (credited as co-author) and
closes #187.

Test plan

• args_test.py: every integrator forwards args and integrates the
  parametric integrand correctly across backends (grid rules exact; MC/VEGAS
  within tolerance); args=None matches a pre-bound lambda — 12 passed
• full integrator sweep (trapezoid/simpson/boole/gauss/monte_carlo/vegas/
  integrator_types) still green — 46 passed
• ruff / pydoclint / vulture clean

Closes #187. Roadmap F3.

[gomezzz]

Claude: Thanks!

• Finding 2: added a comment in vegas.py explaining that VEGAS bakes the integrand into a closure (and evaluates via _eval) rather than routing args through evaluate_integrand, so the None -> () normalization is intentionally local — with a note to keep the two in sync (1d97cac).
• Finding 1 (tutorial): deferring to the F4 docs bundle, whose 'passing parameters' section (issue Example/documentation for parametric domain of integration? #186) is exactly the discoverability fix Integrate function with parameters #187 asked for. I'll add the args=(alpha, beta) parametric example there alongside the QMC and VEGAS-error snippets so all the new-feature docs land together.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
torchquad
__init__.py	25	2	92%	63–64
torchquad/integration
base_integrator.py	49	7	86%	28, 71–74, 78, 113, 117, 122
boole.py	30	3	90%	54, 73–76
gaussian.py	51	3	94%	84, 108, 128
grid_integrator.py	97	3	97%	50, 164, 268
integration_grid.py	49	4	92%	64–65, 132, 135
monte_carlo.py	93	3	97%	79, 101, 230
rng.py	60	7	88%	71–74, 93–94, 102
simpson.py	29	3	90%	52, 71–74
utils.py	131	11	92%	35–36, 102, 173, 177, 184, 196, 198, 204, 299, 306
vegas.py	162	4	98%	102–103, 193, 340
vegas_map.py	103	8	92%	247–257
torchquad/utils
deployment_test.py	192	63	67%	53–55, 65–66, 69–70, 78–79, 91–93, 164, 175–176, 180–181, 183–184, 196–199, 211–213, 221, 232–234, 237, 247, 250, 253, 256–259, 267–275, 280–288, 297–306, 316–323
enable_cuda.py	15	6	60%	17–22
set_log_level.py	14	2	86%	45–46
set_precision.py	34	9	74%	35–38, 50–51, 70–72
TOTAL	1230	138	89%

Tests	Skipped	Failures	Errors	Time
104	0 💤	0 ❌	0 🔥	2m 34s ⏱️