Fix constrained ignored lambdas in Plutus Tx

[knoal]

Summary

Fix the issue-aligned ignored-lambda regression from #6085 by recovering constrained argument types for naked lambdas like \_ _ -> () and \_ _ _ -> () when the surrounding expected type is known.

What changed

• thread an optional expected type from compileMarkedExpr into the initial compileExprWithDefs entrypoint
• when that expected type is available, retag leading erased Any binders in the Core expression before handing control back to the normal expression compiler path
• add TH regressions for the concrete constrained cases that match the reported failure shape:
  • CompiledCode (BuiltinData -> BuiltinData -> ())
  • CompiledCode (BuiltinData -> BuiltinData -> BuiltinData -> ())
• add/update goldens for GHC 9.6 and 9.12

Scope / note on narrowing

During local validation I found that a broader polymorphic TH repro was too wide for a clean-state fix here. This PR intentionally targets the issue-aligned constrained case from #6085, where surrounding context already determines the lambda argument types.

Validation

Local focused validation:

• cabal test --project-file=cabal.project.plugin-tests plutus-tx-plugin-tests --test-options='--accept --pattern=ignoredUntyped'
• cabal test --project-file=cabal.project.plugin-tests plutus-tx-plugin-tests --test-options='--pattern=/TH/'

Both passed locally after the narrowed fix.

Related issue

• Closes Investigate if lambdas not annotated with types fail to compile in Plutus Tx #6085