FR: Garbage collection for dx/subsecond-generated files

A simple request: as things stand, usage of subsecond seems to create a humongous number of files, to the point that deleting the target directory is... intense and slow.

Please correct me if I'm misinterpreting, but if the following files (in much larger number) are created by dx/subsecond during serving, is there something that could be done to help clean these up as the tool continues to run?

```sh
target/wasm32-unknown-unknown/wasm-dev/deps/render-cf0c7bd38bcefb7c.1fzwa891xeyrf27ityrxpduft.01u5yjs.rcgu.thin-lto-after-internalize.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-5d0ea4cefd46e224.1ghphrbem1i01v67qj68iilyw.1sqjljg.rcgu.thin-lto-after-pm.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-067755b81654bb77.5gvt00nj169hb4mlwzv83amzc.10lib2l.rcgu.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-26f6ca62bfac94ad.2ubx8jwghn9mgyoaq8k7xvxtc.1dfdr9k.rcgu.thin-lto-input.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-cf0c7bd38bcefb7c.9okj82safnp6gjg5l4fairta7.09u9u1s.rcgu.thin-lto-input.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-d1bfca76f3eb5533.0dwdv7fbsjil5ihar7apigk1r.199nsnn.rcgu.no-opt.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-086597959240df49.dex5dcu3hxfgaxqb4cst45874.1y37knv.rcgu.thin-lto-input.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-b4678300f121a560.6e705wysacizco7ggtcop0mvc.0mwqtv7.rcgu.thin-lto-after-import.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-a8309e5cef77253b.6581i80czabyuo47q4nixvx3b.0i7ks84.rcgu.thin-lto-after-resolve.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-cf0c7bd38bcefb7c.4micg3ah4lg03f9y3wzpbn09h.15vu6ll.rcgu.thin-lto-after-import.bc
target/wasm32-unknown-unknown/wasm-dev/deps/render-88cbd8402c4609d5.1rev6c73j8lufs5g9nd5hgtg8.0ov2rtm.rcgu.thin-lto-after-rename.bc
```