fix: retain doNothing() stubs inside lambda bodies to prevent uncompilable code

[darrencilia]

What's changed?

Added a guard in RemoveDoNothingForDefaultMocks to skip removal of doNothing() stubs when they appear as an expression lambda body or a switch expression arm, preventing a dangling -> which does not compile.

Block lambda and switch block arm cases are not guarded as removal leaves an empty block which is valid Java and can be cleaned up downstream by static analysis.

What's your motivation?

Fixes #1008

When doNothing().when(mock).method(args) is the expression body of a lambda or
a switch expression arm, removing it leaves a dangling -> which does not compile.

Anything in particular you'd like reviewers to focus on?

The two helpers isExpressionLambdaBody() and isSwitchExpressionArm() confirming the cursor level is correct for each case.

Have you considered any alternatives or workarounds?

An alternative would be to remove the entire enclosing construct when the body becomes empty. However this is a significantly more complex AST transformation and risks unintended behaviour changes. Retaining is the safer option for compile-breaking cases.

Any additional context

The bug surfaces through any recipe that chains through RemoveDoNothingForDefaultMocks, including UpgradeSpringBoot_3_5 and all other composite recipes that include RemoveDoNothingForDefaultMocks as part of their stack.

[darrencilia]

I have updated the oriignal comment and Issue to include my latest commit changes.

For this I added 6 tests:

• retainsDoNothingInsideLambdaBody - expression lambda, recipe makes no change
• removesDoNothingInLambdaBlockLeavingEmptyBlock - block lambda sole statement, recipe removes and leaves empty block
• removesDoNothingWhenNotSoleStatementInLambdaBlock - block lambda multiple statements, recipe removes correctly
• retainsDoNothingInSwitchExpressionArm - switch arrow arm, recipe makes no change
• removesDoNothingInSwitchExpressionArmBlockLeavingEmptyBlock - switch block arm sole statement, recipe removes and leaves empty block
• removesDoNothingWhenNotSoleStatementInSwitchExpressionArmBlock - switch block arm multiple statements, recipe removes correctly

[timtebeek]

Thanks again for the help here and the clear test examples. I've inline the small methods just to have fewer indirections when reading the code. We'll merge as soon as CI is green.