Update checkExpressions

[DeHopen]

I have optimized the checkExpressions method in the CurlyBracketsStructureCheck class. Instead of looping through all EXPR nodes, FluentIterable is now used to filter only those nodes that are on the first or last row of the block. This reduces the number of iterations and makes the code more readable and declarative.

Reasons for the change:

• Reducing the number of iterations: Previously, the code checked each node, even if it was not on the first or last line. Now we filter only the necessary nodes, which speeds up the execution.
• Improved readability: Using FluentIterable makes the code more declarative and understandable, as it is clearly visible that we are filtering nodes according to a certain condition.
• Following modern practices: Using a functional style with FluentIterable is consistent with modern Java development practices.

[DeHopen]

@yegor256

CI is green

[DeHopen]

@yegor256 ping

[DeHopen]

@yegor256 ping

[DeHopen]

@yegor256 ping

[yegor256]

@DeHopen I don't see enough motivation for this change