Simultaneous builds are unreliable

Hi, foremost, thank you for this tool, it helped me quite a lot.

I use it in a CI pipeline, and it builds two versions of the same script (with some modules being replaced).
When I tried to optimize the duration it takes, I changed to building the two versions simultaneously, that actually does save time. But once every 15 runs I get this error:
```
Error: ENOENT: no such file or directory, rename './node_modules/.cache/.rts2_cache_umd/rpt2_4ac624c30e398d7abd448e108f7ef395666c7280/code/cache_' -> './node_modules/.cache/.rts2_cache_umd/rpt2_4ac624c30e398d7abd448e108f7ef395666c7280/code/cache'
Error: ENOENT: no such file or directory, rename './node_modules/.cache/.rts2_cache_umd/rpt2_4ac624c30e398d7abd448e108f7ef395666c7280/code/cache_' -> './node_modules/.cache/.rts2_cache_umd/rpt2_4ac624c30e398d7abd448e108f7ef395666c7280/code/cache'
at Object.renameSync (node:fs:1026:3)
at RollingCache.roll (/---/scripts/node_modules/rollup-plugin-typescript2/dist/rollup-plugin-typescript2.cjs.js:29229:26)
```
I tracked it down to [this line](https://github.com/developit/microbundle/blob/master/src/index.js#L539C1-L539C65)
which explains what happens. When more than one microbundle script is running, it instructs typescript to use the same cache directory and most likely starts to mess up or rename files that the other version already deleted.

My probosals:
- implement a flag to disable this type of caching, or use a random string for the cacheRoot
- generate a simple hash of the arguments provided and use that in combination of cacheRoot, this will prevent two scripts doing different jobs of interfering with each other

Please let me know if you would accept a PR for either of those implementations

Start at src/index.js around line 539 and inspect how the cache directory is supplied to rollup-plugin-typescript2. Reproduce two simultaneous microbundle builds in the CI-style setup, then verify that concurrent builds no longer produce the reported ENOENT rename failure, either by disabling the cache or separating cache locations.

Written by the indexing model from the issue text.