perf: Reduce template compilation time by ~16%

[willbeason]

Remove unnecessarily parsing Rego multiple times. Converting to/from the parsed Rego AST is expensive, so removing this results in a significant speedup in compilation times.

Before:

constraint$ GOMAXPROCS=1 go test ./pkg/client --bench=AddTemplate$/^Complex
goos: linux
goarch: amd64
pkg: github.com/open-policy-agent/frameworks/constraint/pkg/client
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkClient_AddTemplate/Complex/1_Templates         	     776	   1503423 ns/op
BenchmarkClient_AddTemplate/Complex/2_Templates         	     396	   3006789 ns/op
BenchmarkClient_AddTemplate/Complex/5_Templates         	     154	   7659658 ns/op
BenchmarkClient_AddTemplate/Complex/10_Templates        	      76	  15719632 ns/op
BenchmarkClient_AddTemplate/Complex/20_Templates        	      36	  32558251 ns/op
BenchmarkClient_AddTemplate/Complex/50_Templates        	      13	  84629914 ns/op
BenchmarkClient_AddTemplate/Complex/100_Templates       	       6	 173179630 ns/op
BenchmarkClient_AddTemplate/Complex/200_Templates       	       3	 355320224 ns/op
PASS
ok  	github.com/open-policy-agent/frameworks/constraint/pkg/client	12.063s
constraint$ GOMAXPROCS=1 go test ./pkg/client --bench=AddTemplate$/^Complex --benchmem
goos: linux
goarch: amd64
pkg: github.com/open-policy-agent/frameworks/constraint/pkg/client
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkClient_AddTemplate/Complex/1_Templates         	     777	   1502605 ns/op	  546829 B/op	   11315 allocs/op
BenchmarkClient_AddTemplate/Complex/2_Templates         	     385	   3006709 ns/op	 1089453 B/op	   22592 allocs/op
BenchmarkClient_AddTemplate/Complex/5_Templates         	     157	   7581477 ns/op	 2718134 B/op	   56424 allocs/op
BenchmarkClient_AddTemplate/Complex/10_Templates        	      76	  15584239 ns/op	 5441096 B/op	  112825 allocs/op
BenchmarkClient_AddTemplate/Complex/20_Templates        	      37	  31969236 ns/op	10882470 B/op	  225619 allocs/op
BenchmarkClient_AddTemplate/Complex/50_Templates        	      13	  82900329 ns/op	27158004 B/op	  563895 allocs/op
BenchmarkClient_AddTemplate/Complex/100_Templates       	       6	 172543024 ns/op	54392817 B/op	 1127905 allocs/op
BenchmarkClient_AddTemplate/Complex/200_Templates       	       3	 361875473 ns/op	108725650 B/op	 2255664 allocs/op

After:

constraint$ GOMAXPROCS=1 go test ./pkg/client --bench=AddTemplate$/^Complex
goos: linux
goarch: amd64
pkg: github.com/open-policy-agent/frameworks/constraint/pkg/client
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkClient_AddTemplate/Complex/1_Templates         	     910	   1263631 ns/op
BenchmarkClient_AddTemplate/Complex/2_Templates         	     478	   2484350 ns/op
BenchmarkClient_AddTemplate/Complex/5_Templates         	     183	   6491906 ns/op
BenchmarkClient_AddTemplate/Complex/10_Templates        	     100	  13091745 ns/op
BenchmarkClient_AddTemplate/Complex/20_Templates        	      46	  26967734 ns/op
BenchmarkClient_AddTemplate/Complex/50_Templates        	      16	  70383262 ns/op
BenchmarkClient_AddTemplate/Complex/100_Templates       	       7	 144370954 ns/op
BenchmarkClient_AddTemplate/Complex/200_Templates       	       4	 312258998 ns/op
PASS
ok  	github.com/open-policy-agent/frameworks/constraint/pkg/client	12.309s
constraint$ GOMAXPROCS=1 go test ./pkg/client --bench=AddTemplate$/^Complex --benchmem
goos: linux
goarch: amd64
pkg: github.com/open-policy-agent/frameworks/constraint/pkg/client
cpu: Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz
BenchmarkClient_AddTemplate/Complex/1_Templates         	     930	   1278016 ns/op	  455831 B/op	    9200 allocs/op
BenchmarkClient_AddTemplate/Complex/2_Templates         	     466	   2514157 ns/op	  907062 B/op	   18360 allocs/op
BenchmarkClient_AddTemplate/Complex/5_Templates         	     186	   6472272 ns/op	 2263255 B/op	   45847 allocs/op
BenchmarkClient_AddTemplate/Complex/10_Templates        	     100	  13266355 ns/op	 4526045 B/op	   91662 allocs/op
BenchmarkClient_AddTemplate/Complex/20_Templates        	      43	  27157279 ns/op	 9061271 B/op	  183310 allocs/op
BenchmarkClient_AddTemplate/Complex/50_Templates        	      16	  70915101 ns/op	22633622 B/op	  458174 allocs/op
BenchmarkClient_AddTemplate/Complex/100_Templates       	       7	 146138294 ns/op	45285475 B/op	  916346 allocs/op
BenchmarkClient_AddTemplate/Complex/200_Templates       	       4	 303379543 ns/op	90568002 B/op	 1832689 allocs/op

[codecov-commenter]

Codecov Report

Merging #206 (2b1fee9) into master (acd7764) will decrease coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #206      +/-   ##
==========================================
- Coverage   46.65%   46.28%   -0.37%     
==========================================
  Files          64       64              
  Lines        2840     2815      -25     
==========================================
- Hits         1325     1303      -22     
  Misses       1295     1295              
+ Partials      220      217       -3     

Flag	Coverage Δ
unittests	46.28% <ø> (-0.37%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...eworks/constraint/pkg/regorewriter/regorewriter.go	73.41% <0.00%> (-1.27%)	⬇️
...orks/constraint/pkg/client/drivers/local/driver.go	42.33% <0.00%> (-0.61%)	⬇️
...s/constraint/pkg/client/drivers/local/compilers.go	65.62% <0.00%> (-0.38%)	⬇️
...t/frameworks/constraint/pkg/client/rego_helpers.go
...eworks/constraint/pkg/client/drivers/local/rego.go	50.00% <0.00%> (ø)

---

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[willbeason]

Ultimately this is just refactoring - no visible changes to users or consumers of this library.

[maxsmythe]

LGTM

[sozercan]

LGTM

[willbeason]

Tested locally via go.work - passes in Gatekeeper.