Give `Reduce` and `TapLinear` unique IDs

[casey]

Fixes #77. I don't think this actually matters, but it helps if someone is trying to understand what IDs are for, since if there are duplicate IDs, a reader might think that it's for some reason.

To find duplicate IDs:

rg -IN 'const ID: u64 = \d+' --only-matching | sort | uniq -c | sort -n

To find unassigned IDs:

rg -IN 'const ID: u64 = \d+' --only-matching | sort | uniq | cut -d' ' -f5 > ids.txt
comm -23 <(seq 0 100) <(sort -n ids.txt)

After this PR, the only unassigned two-digit IDs are 27, 37, 59, and 99.