ucm: add Repeat block - repetitive pattern substitution (Syntax 9)

ucm: add Repeat block - repetitive pattern substitution (Syntax 9)

Implements Repeat blocks for generating repetitive configuration patterns
with variable substitution. This feature allows applying a configuration
block multiple times with different variable values, significantly reducing
duplication in UCM configuration files.

iterator abstraction allows easy extension for future pattern types.

Example:

  Repeat.VolumeInit {
    Pattern {
      Variable 'ch'
      Type Integer
      First 0
      Last 7
      Step 1
    }
    Apply {
      cset "name='PCM Channel ${var:ch} Volume' 100%"
    }
  }

Signed-off-by: Jaroslav Kysela <perex@perex.cz>