Fix: separate Split Bregman inner solver options

[AHMETHAKANBEZIR1]

Fixes #815.

Outer tol/rtol/rtol1 consume names needed by inner CGLS, preventing callers from configuring its stopping criteria. Add keyword-only kwargs_solver to splitbregman and SplitBregman.solve; its entries override duplicate legacy keywords without modifying the caller's dictionary.

Following review, name the compatibility catch-all **kwargs, document its planned removal in v3.0.0, and use the merged kwargs_solver consistently. Simplify the parameter documentation and show only the SciPy LSQR options actually used in the TV example.

Keep eight focused new cases using the function API and the suite's backend-aware np/assertion helpers. The CGLS accuracy and precedence tests use one outer/one inner iteration and an independent dense normal-equation solution. The relative-tolerance test documents its distinct purpose: outer rtol/rtol1 configure cost callbacks, while inner CGLS thresholds are passed through kwargs_solver.

Validation on Windows CPU / Python 3.12.14 / NumPy 2.5.4 / SciPy 1.18.1:

• All 19 Split Bregman cases passed, including the eight new focused cases.
• The complete sparsity module produced 100 passes and seven SPGL1 failures. All seven failures reproduce on the unchanged pre-review head 658d234 with the same environment (spgl1.py:927, np.isreal(A).all() returns a Python bool). They are not claimed resolved; no test skips or unrelated dependency changes were added.
• The TV example completed from examples/ with Agg, exit 0. Configured pre-commit checks and diff checks passed.
• GPU/CuPy, the full package suite and the full documentation build were not run locally. All five refreshed checks for b2143b8 passed, including Windows, Linux, Mac, Codacy and documentation.

AI disclosure: prepared and tested autonomously with OpenAI Codex. No independent human review is claimed.

[codacy-production]

Up to standards ✅

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[mrava87]

@AHMETHAKANBEZIR1 thanks for the contribution 😄

I provided some comments, mostly on tests needed some cleanup to make sure they are more in line to the other tests in the suite.