Validate fixed-size parameter defaults during generation

[Daniiiil1]

Summary

• reject fixed-capacity defaults that exceed the generated rsl::StaticVector or rsl::StaticString capacity
• validate a configured fixed_size<> constraint against the default during code generation
• preserve the current bounded-capacity semantics, so shorter defaults remain valid unless fixed_size<> requires an exact length
• cover integer, double, and string arrays as well as fixed strings

This avoids generating code that can hit an rsl::StaticVector assertion before runtime validation runs. It also keeps the existing rsl containers and their ROS parameter assignment behavior.

Fixes #342

Testing

• 27 Python generator tests passed
• Black check with --skip-string-normalization passed
• git diff --check passed