require("IRReceiver") - out of memory (eventually)

The remotes I have seem to send 1's after fixed length (33 bytes in most cases) as repeat code if a button is constantly hit

Yes, but they do this after a gap - which if (d>0.04) should normally pick up? Perhaps it's one of those ESP8266 gotchas again - after all, this module's been around for years and nobody has reported a problem with it before.

Potentially you could have a varying length, but it does complicate usage - and you might want to use the same receiver to detect different types of remote controls which have different signal lengths.

I've bee also thinking about how the codes could be shortened instead of sending a string of 1 and 0's, perhaps a hex code?

It's done this way for speed of processing - single character string appends are nice and fast, so I wouldn't advise changing it.

Realistically bits come in once a millisecond maximum, so to fill up available memory 0 even on an ESP8266 - you've got to have a continuous burst of 10 seconds of IR. I think that's so unlikely that memory efficiency isn't really an issue.

What's the 'fluro lamp' that's triggering the receiver, and are you using a proper receiver?

Maybe you could check getPinMode on the receiver pin, to make sure it really is in input_pullup mode.

Most receivers need a ~40kHz series of IR pulses to trigger, and then to run out of memory there needs to not be a gap of more than 40ms for a whole 10 seconds. It all seems really unlikely unless something is wrong.