alignment of subnumcases in the page

I want to label each case in cases so I used subnumcases environment.However, it seems like what is centered is the first letter, not the entire chunk.

I made a MWE with the packages I need for my work, and by toggling off the packages one by one, I found that mathtoolscellspaceempheq are causing the ugly alignment.(for empheq, maybe I can go without it.)

This is the MWE script:

\documentclass[12pt]{article}\usepackage[top=2.5cm, left=2.5cm, right=2.5cm, bottom=3cm]{geometry}\usepackage{amsmath,amsfonts}\usepackage{showframe}\usepackage{cases}% when any of the packagages below(mathtools, cellspace, empheq) is used, it gives the ugly output like in the screenshot. \usepackage{mathtools}%\usepackage{cellspace}%\usepackage{empheq}\begin{document}    %%%%%%%%%%%%%%%%%%%%%%%     When using {\bfseries subnumcases environment} with mathtools, cellspace, or empheq, it seemas like its starting point is centered    \begin{subnumcases}{f(x)=}        x & $0<x<1$ \\        1000000000000000000000000000x  & $1\leq x$    \end{subnumcases}    But {\bfseries cases environment} is okay and and I want the alignment of subnumcases also to be like this.    \begin{equation}        f(x)=        \begin{cases}            x & 0<x<1 \\            1000000000000000000000000000x  & 1\leq x        \end{cases}    \end{equation}    %%%%%%%%%%%%%%%%%%%%%%% \end{document}

And this is my ugly output with mathtools:

How can I have center-aligned subnumcases environment while using mathtoolscellspaceempheq packages?

Thanks!

P.S. if you have any other way to have sub-numbers for cases, it's also welcome.I tried subequations, but found difficulty to put it in case for like "f(x) = { " part at the left of the subequations chunk.

+ I'm using texstudio and I'm adding the screenshot of the compiled output in texstudio.