Name incomplete reactions and their remedy for adaptive tau

[jc-macdonald]

Adaptive tau-leaping requires complete molecular reactant metadata. Two problems with how it reported missing metadata:

• It failed only at run time, without saying which reactions were incomplete.
• It advised adding an explicit reactants list to every op_system transition. Since op_system #251, transitions generated by chain: and coord_shift declare catalysts instead, and coord_shift rejects reactants. So the advice could not be followed for exactly the models #251 targets.

No op_engine test covered adaptive tau-leaping on generated reactions.

Closes #188.

Behavior

• Compiled network: CompiledReactionNetwork.incomplete_reactions names the selected reactions without complete metadata.
• Error message: both the run-time error and a new validate_system issue (incomplete_reactants) list those reactions, in declaration order. They give both remedies: reactants on ordinary transitions, or catalysts on chain: and coord_shift entries. The message keeps the phrase "complete molecular reactant metadata" that existing callers match.
• Hybrid mode: validation checks only the selected stochastic_reactions, matching what the network compiles.
• No dependency change: the development pins are already on op_system main (#252 merge).

Coverage

• Declared catalysts: an age-structured SIR with a two-stage chain: infectious period (entry.catalysts lists both stages, and the chain's catalysts: []) and axis-wide aging over all four compartments (catalysts: []). It publishes seven complete reactions and validates cleanly. Under adaptive tau-leaping it keeps integer, non-negative states, a non-increasing total (aging out of the last bin is absorbing), and produces recoveries.
• Without declarations: validation reports one incomplete_reactants issue naming every generated reaction and both remedies, and run raises with the same list.
• Hybrid selection: reports only the selected reaction.

Docs

• Provider README, adaptive tau-leaping paragraph: catalysts for generated transitions.
• CHANGELOG entry under Unreleased.

Validation

• just ci: 592 core tests passed, 2 skipped. 379 provider tests passed (3 new). Ruff and strict mypy passed for both packages.
• just docs: strict documentation build passed.

Two commits: 222 and 10 changed lines.

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