Chore: src/neg_tests cleanups

[jmid]

While trying out #329 on selected parts of the test suite locally I discovered a couple of needless dependencies in src/neg_tests. This PR seeks to remove them:

• Our src/neg_tests/lin Thread tests depended on lin_common* files both needlessly requiring Domains - and so we move the Lin_domain functor applications to the Domain-driver files
• The src/neg_tests/stm_tests* had a qcheck dependency rather than requiring qcheck-core and so we switch to using QCheck_base_runner like the rest of the test suite.

[jmid]

CI summary:

• Win bytecode 5.1 failure to trigger Out_channel issue
• Cygwin trunk part1 timeout due to excessive runtimes of multiple Lin Domain tests (BigArray1,Atomic,Bytes,Ephemeron,Out_channel)
• Win trunk and Win bytecode 5.1 + trunk threadomain deadlocks
• Cygwin trunk part2 failure to trigger STM int ref test parallel asymmetric
• Cygwin 5.1 part2 timeout due to excessive runtime of two tests: Sys STM test and Lin DSL Weak HashSet test with Domain
• Cygwin 5.1 part2 timeout due to excessive test runtime of Lin DSL Weak HashSet test with Domain incl. failure to trigger STM int64 ref test parallel asymmetric

None of these are related to this PR so I'll merge.