Just setting https_proxy isn't going to give you any caching benefits for https requests and isn't going to MITM TLS in any way. The client will make a CONNECT

Just setting https_proxy isn't going to give you any caching benefits for https requests and isn't going to MITM TLS in any way. The client will make a CONNECT request through to the destination and the encryption is end to end and the response not cacheable by the proxy.