To build a plugin, run make build, which will produce mev.so.
To use a built mev.so, edit your seid's app.toml. Replace handler_plugin_path under the mev section to your mev.so's path, then restart seid.
In order for a Go plugin to work, the dependencies of the host program and the plugin should be the same. It is recommended that the plugin owner copy the entirety of sei-chain's go.mod to their plugin's go.mod whenever sei-chain is upgraded, and rerun go mod tidy && make build for their plugin.