Adds basic libfuzzer harness

[nathaniel-brough]

This harness simply mounts and unmounts a ramdisk
that is populated by fuzzed data. This fuzz harness tests that littlefs is able to safely attempt to
mount a corrupted storage device.

[geky]

Just a quick note about the CI failures, you'll need to rebase/retarget onto the devel branch for things to work correctly.

GitHub made a breaking change to their APIs somewhat recently and it's made things a bit of a mess.

[nathaniel-brough]

Just a quick note about the CI failures, you'll need to rebase/retarget onto the devel branch for things to work correctly.

Done

[geky-bot]

Tests passed ✓, Code: 17064 B, Stack: 1440 B, Structs: 812 B

	Code	Stack	Structs		Coverage
Default	17064 B	1440 B	812 B	Lines	2394/2574 lines
Readonly	6194 B	448 B	812 B	Branches	1245/1584 branches
Threadsafe	17924 B	1440 B	820 B		Benchmarks
Multiversion	17124 B	1440 B	816 B	Readed	29369693876 B
Migrate	18760 B	1744 B	816 B	Proged	1482874766 B
Error-asserts	17748 B	1432 B	812 B	Erased	1568888832 B