Preference.Any uses SCIP if gurobi license is restricted. Add GurobiRestriced for explicit opt in to the restricted license

[tlambert03]

fixes #74

cc @cmalinmayor

gurobipy	License state	_have_gurobi_license()	Any	Scip	Gurobi	GurobiRestriced
✓	real valid license	True	Gurobi	Scip	Gurobi	Gurobi
✓	GRB_LICENSE_FILE=/nonexistent	False	Scip	Scip	raises	raises
✓	GRB_LICENSE_FILE=/malformed (stale CI)	False	Scip	Scip	raises	raises
✗	n/a	False	Scip	Scip	raises	raises
✓	bundled pip license only	False	Scip ✓#74	Scip	raises	Gurobi (size-limited)

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.59%. Comparing base (0fdfae7) to head (fc960b1).
⚠️ Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ilpy/solver_backends/__init__.py	94.73%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   75.72%   83.59%   +7.87%     
==========================================
  Files          17       11       -6     
  Lines         828      829       +1     
  Branches      154        0     -154     
==========================================
+ Hits          627      693      +66     
  Misses        136      136              
+ Partials       65        0      -65     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.