Improve performance of logdensity computation

[sunxd3]

No description provided.

[github-actions]

BridgeStan not found at location specified by $BRIDGESTAN environment variable, downloading version 2.5.0 to /home/runner/.bridgestan/bridgestan-2.5.0
Done!
Model dogs produces error: ErrorException("log_density() failed with exception: Exception: bernoulli_lpmf: Probability parameter is inf, but must be in the interval [0, 1] (in '/home/runner/work/JuliaBUGS.jl/JuliaBUGS.jl/benchmark/stan/bugs_examples/vol1/dogs/dogs.stan', line 37, column 6 to line 38, column 62)\n")

Model	Parameter Count	Data Count	Stan Density Time (µs)	Stan Density Gradient Time (µs)	JuliaBUGS Density Time with Graph Walk (µs)	JuliaBUGS Density Gradient Time with ReverseDiff.jl(compiled tape) (µs)
rats	65	150	5.7026	8.34567	280.256	88.544
pumps	12	10	1.00566	1.38214	29.525	7.76133
dogs	2	720	NA	NA	767.848	148.186
seeds	26	21	2.45458	3.22822	71.132	19.837
surgical_realistic	14	12	1.26626	1.72544	40.685	8.569
magnesium	108	96	10.525	12.373	393.096	84.297
salm	22	18	2.36608	2.99556	59.271	12.468
equiv	15	20	2.49273	3.35625	48.159	15.85
dyes	9	30	0.992929	1.33932	30.466	15.639
stacks	6	21	1.13327	1.71435	95.437	15.198
epil	303	236	33.953	39.584	885.286	253.662
blockers	47	44	3.22933	3.6555	164.326	30.797
oxford	244	240	16.12	18.8345	1055.34	206.985
lsat	1006	5000	180.635	222.513	10099.5	1376.2
bones	33	422	73.486	90.638	2587.04	192.037
mice	20	65	7.316	9.49433	79.2325	40.094
kidney	64	58	10.74	16.311	181.923	76.832
leuk	18	714	20.598	26.75	838.69	233.885
leukfr	40	714	24.135	31.939	981.591	240.878

[coveralls]

Pull Request Test Coverage Report for Build 11515715686

Details

• 28 of 29 (96.55%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 77.821%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/model.jl	28	29	96.55%

Totals
Change from base Build 11494108749:	0.1%
Covered Lines:	1386
Relevant Lines:	1781

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💛 - Coveralls

[sunxd3]

this PR reduces the logdensity evaluation time of Rats from 6ms to about 0.3ms (#227 (comment))