acc: record configuration edge cases ahead of the libs/dyn removal

[denik]

Changes

Twenty bundle validate acceptance tests under acceptance/bundle/validate/parity/, each pinning current behaviour for a configuration edge case:

• merge keys and aliases in targets.*.variables (inherited through a target or root <<, aliases of a complex default, duplicate and malformed <<, inline mappings),
• duplicate keys, timestamps as shorthands or nested in complex defaults,
• references that resolve to the wrong type inside lists and maps,
• includes overriding fields with "" / 0 / false, diagnostics after a failed include merge,
• resources: null, targets: false, schedule: null,
• diagnostic locations for unknown fields in complex variables and duplicated app resources.

Badness marks the ten cases where current behaviour is itself wrong:

• a timestamp nested in a complex default fails with an internal error; a timestamp shorthand is dropped;
• an inline mapping as the merge value is rejected although the YAML spec allows it;
• duplicate keys are accepted silently (the later one wins);
• an empty resources: section is an error without a location (empty targets, variables, sync are fine); targets: false fails with an internal "failed to rewrite" message;
• an explicitly null schedule is reported as missing its required fields;
• an unknown field in a complex variable default is reported at the resource using the variable;
• diagnostics of includes after a failed merge are hidden.

Why

They guard behaviour ahead of #6954, which replaces libs/dyn: all twenty currently produce different output there.

Tests

Goldens recorded on main.

This pull request and its description were written by Isaac.

[eng-dev-ecosystem-bot]

Integration test report

Commit: cd9e915

Run: 38895069547

	Env	✅​pass	🙈​skip	Time
✅​	aws linux-2core-8gb	276	35	5:28
✅​	aws-windows-latest-4core-16gb	278	33	3:29
✅​	azure linux-2core-8gb	275	35	5:19
✅​	azure-windows-latest-4core-16gb	277	33	3:43
✅​	gcp linux-2core-8gb	276	35	5:08
✅​	gcp-windows-latest-4core-16gb	278	33	3:32

Top 6 slowest tests (at least 2 minutes):

duration	env	testname
3:53	aws linux-2core-8gb	TestAccept
3:46	gcp linux-2core-8gb	TestAccept
3:41	azure linux-2core-8gb	TestAccept
3:37	azure-windows-latest-4core-16gb	TestAccept
3:26	gcp-windows-latest-4core-16gb	TestAccept
3:22	aws-windows-latest-4core-16gb	TestAccept