but unfortunately the module seems outdated and does not install: Mojolicious::Plugin::Cache. In CGI, such a solution is implemented in CGI::Buffer, and Cache::Cache.

Hello

Your question also contains the answer ;)

Mojo has https://metacpan.org/pod/Mojolicious::Plugin::CHI but it doesn't have the same sugar as Dancer::Plugin::Cache::CHI

get '/mods/perltidy/:modname' => sub { 
    my $ret =  src2perltidy( params ) ;
    redirect "/mods" if not defined $ret or not length $ret;
    cache_page $ret;
};
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