The version-rolling.min-bit-count field was previously documented as a TMask return value, even though the examples and real-world usage treat it as a request parameter with an integer bit count.
This change moves version-rolling.min-bit-count to the extension parameters section and changes its type to Integer (>= 0), keeping the original explanatory text. This makes the specification consistent with the JSON examples and with existing implementations of the stratum protocol extension.
