debian: add the DEP-8 tests-control parser

Parse debian/tests/control into runnable test descriptions: one test
per Tests: script and per Test-Command value, carrying the shared
Depends/Restrictions/Tests-Directory stanza fields and the autopkgtest
command1 enumeration (test-name overrides advance the counter).
Depends substitution is deliberately left raw: expanding @ and friends
needs the built binary list, so it belongs to the runner.

First piece of pkh test (see plans/pkh-test.md); the runner expands
these stanzas against the deb822 primitives.

src/debian/mod.rs

@@ -10,6 +10,7 @@
 //! - [`files`]: `debian/files` artifact registry (`Dpkg::Dist::Files`)
 //! - [`version`]: Debian version splitting/validation/comparison
 //! - [`changelog`]: `debian/changelog` entry parsing
+//! - [`tests_control`]: DEP-8 test metadata (`debian/tests/control`)
 
 pub mod arch;
 pub mod changelog;
@@ -17,6 +18,7 @@ pub mod checksums;
 pub mod control;
 pub mod deps;
 pub mod files;
+pub mod tests_control;
 pub mod version;
 
 pub use changelog::{
@@ -28,4 +30,5 @@ pub use control::{
     ControlInfo, Paragraph, parse_paragraphs, strip_clearsigned_armour, write_paragraph,
 };
 pub use files::{FilesEntry, FilesList};
+pub use tests_control::{Test, TestsControl};
 pub use version::DebianVersion;