6.
已知函数\(f(x)\),当\(x\),\(y\in R\)时,恒有\(f(x+y)=f(x)+f(y).\)当\(x > 0\)时,\(f(x) > 0\)
\((\)Ⅰ\()\)判断函数\(f(x)\)的奇偶性和单调性,并证明;
\((\)Ⅱ\()\)是否存在\(m\),使\(f\left( 2{{\left( {{\log }_{2}}x \right)}^{2}}-4 \right)+f\left( 4m-2\left( {{\log }_{2}}x \right) \right) > 0\)对于任意\(x\in [1,2]\)恒成立?若存在,求出实数\(m\)的取值范围;若不存在,说明理由.