fix(solve): init and initial_guess together raise "Conflicting aliases" in descriptive mode

[ocots]

Closes #964.

Problem

solve(ocp; init=1, initial_guess=2) in descriptive mode reported Unknown option :init with unrelated suggestions (:mu_init, :max_iter, …). Explicit mode already reported "Conflicting aliases". CTBase's route_all_options → Options.extract_option consumes the first alias found and leaves the other one in kwargs. The leftover alias is then routed to the strategies.

Change

• The conflict check of _extract_action_kwarg is now its own helper, _check_action_aliases(kwargs, names) (src/helpers/kwarg_extraction.jl). Explicit mode calls it through _extract_action_kwarg, as before.
• _route_descriptive_options calls it on _INITIAL_GUESS_ALIASES before route_all_options.
• Docs, page "Initial guess", section "init or initial_guess": states the error raised in both modes instead of describing the bug.
• CHANGELOG entry under [Unreleased].

Output after the fix, for the reproducer of the issue, both modes:

IncorrectArgument → _check_action_aliases, kwarg_extraction.jl:122
│  Conflicting aliases for the same option
│  Got       multiple aliases [:initial_guess, :init] provided simultaneously
│  Expected  at most one of (:initial_guess, :init)
│  Hint      Use only one alias at a time, e.g. `init=x0` or `initial_guess=x0`
└─

Choices made

1. Check before routing, not extract before routing. The issue suggests extracting the action options before routing. I only check the aliases and leave extraction to route_all_options. Extracting display up front would bypass its documented priority rule with route_to (_descriptive_action_defs: a strategy can also declare display). The minimal check fixes the bug and changes nothing else.
2. Only initial_guess/init is checked. It is the only action option with an alias; display has none. Adding an alias later means adding it to the call in _route_descriptive_options. I did not build a generic loop over _descriptive_action_defs() for a single case.
3. Fixed here, not in CTBase. The root cause is generic: CTBase.Options.extract_option silently accepts two aliases of one option. That affects every strategy option with aliases (e.g. backend/adnlp_backend), not only the action options. A CTBase fix would need a release and a compat bump, so this PR fixes the user-visible bug now. A follow-up issue on CTBase is worth opening (not done here). Once fixed upstream, _check_action_aliases in descriptive mode becomes redundant but harmless.
4. Same error, same context. The error text is unchanged (context="solve - action option extraction"), so both modes print the same message.

Tests

• test/suite/helpers/test_kwarg_extraction.jl: unit tests of _check_action_aliases (none / one / both present).
• test/suite/solve/test_descriptive_routing.jl: regression tests on _route_descriptive_options and solve_descriptive with init + initial_guess. They check that the message says "Conflicting aliases" and not "Unknown option": both are IncorrectArgument, so the type alone would not catch the bug.

Ran locally: test_kwarg_extraction, test_descriptive_routing and test_explicit give 171/171 passing. The issue's reproducer (without Ipopt, the error is raised before the solve) gives the output above in both modes. The full suite was not run locally.

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