File updates in quick succession leads to unnecessary builds

[matt2e]

Steps to repro:

• run ftl dev with some modules
• start editing the code for a module
• make a small change, save the file, and repeat a few times in quick succession

FTL will queue up all these builds for the same module. After the last save, ftl will have a few of these in the queue. FTL will then build this same module a few times with the same result each time, which is unnecessary.
Possibly, we could look at the existing build to see if it started after the current message, as that would indicate the file change had already been included in the current build.