Pretty cursors

[alexreinking]

After #279 and #280 are merged, this should be rebased onto master.

Implements pretty printing for (internal) cursors. This will be useful for writing tests regarding cursors and cursor forwarding more accurately, as well as for interactive debugging.

Cursor types implemented:

• Nodes
• Gaps
• Blocks

Ultimately, this will be transformed such that cursors can be rendered like so. Consider this proc:

@proc
def bar(n: size, m: size):
    x: f32
    for i in seq(0, n):
        for j in seq(0, m):
            x = 0.0
            x = 1.0
            x = 2.0
            x = 3.0
            x = 4.0
            x = 5.0

A cursor to for i in seq(0, n) would look like:

def bar(n: size, m: size):
    ...
    for i in seq(0, n):  # <-- NODE
        ...

Or to the gap before it:

def bar(n: size, m: size):
    x: f32 @ DRAM
    [GAP]
    for i in seq(0, n):
        ...

The block containing x = 1.0; _ ; x = 3.0 looks like:

def bar(n: size, m: size):
    ...
    for i in seq(0, n):
        for j in seq(0, m):
            ...
            # BLOCK START
            x = 1.0
            x = 2.0
            x = 3.0
            # BLOCK END
            ...

This way we can use golden outputs to very quickly check that cursors are correct.

[codecov-commenter]

Codecov Report

Merging #281 (60578f0) into pretty-print (e44103f) will decrease coverage by 0.02%.
The diff coverage is 89.68%.

@@               Coverage Diff                @@
##           pretty-print     #281      +/-   ##
================================================
- Coverage         87.90%   87.87%   -0.03%     
================================================
  Files                72       72              
  Lines             15509    15632     +123     
================================================
+ Hits              13633    13737     +104     
- Misses             1876     1895      +19     

Impacted Files	Coverage Δ
src/exo/LoopIR_pprint.py	80.26% <83.07%> (+0.37%)	⬆️
src/exo/internal_cursors.py	95.62% <88.88%> (-0.38%)	⬇️
tests/test_internal_cursors.py	100.00% <100.00%> (ø)
tests/test_x86.py	98.36% <0.00%> (-1.64%)	⬇️
src/exo/LoopIR_compiler.py	94.31% <0.00%> (-0.57%)	⬇️

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