dnsimple / erldns / 20745797227

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Add dependency validation and introspection for pipeline pipes (#293)

This commit introduces a mechanism to explicitly declare and validate
dependencies between pipes in the `erldns_pipeline`. It ensures that the
pipeline configuration respects the execution order required by specific
modules.

1. Pipe Dependency Management

Added a new optional callback `c:deps/0` to the `erldns_pipeline`
behaviour. Pipes can now declare:

- `prerequisites`: A list of modules that must appear earlier
- `dependents`: A list of modules that must appear later

The `erldns_pipeline:store_pipeline/2` function has been updated to
`validate_and_prepare/1`. It now validates these constraints at load
time. If a dependency is violated (e.g., a prerequisite is missing or
appears after the dependent pipe), the pipeline initialization will fail
with a useful error message (e.g., unsatisfied_dependency).

2. Introspection

Added `erldns_pipeline:is_pipe_configured/1` and
`erldns_pipeline:is_pipe_configured/2`. These functions allow the system
to check if a specific module or function pipe is present in the main
packet_pipeline or a custom pipeline, enabling dynamic checks at
runtime.

3. Implementations

Updated existing core pipes to utilize the new dependency system:

- `erldns_dnssec`: declares `erldns_resolver` as a prerequisite.
- `erldns_resolver`: declares `erldns_questions` as a prerequisite and
  `erldns_sorter`, `erldns_section_counter` as dependents.

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