Further improve performance of logdensity evaluation

[sunxd3]

A source of type instability is the prepare_arg_values. This PR removes this function by modifying node functions to take evaluation_env directly and unpack within node functions, thus save the lookup and constructing keyword arguments step.

[coveralls]

Pull Request Test Coverage Report for Build 11730210167

Details

• 58 of 66 (87.88%) changed or added relevant lines in 4 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 75.054%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/model.jl	44	52	84.62%

Files with Coverage Reduction	New Missed Lines	%
src/model.jl	2	82.51%

Totals
Change from base Build 11651689911:	-0.2%
Covered Lines:	1387
Relevant Lines:	1848

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💛 - Coveralls

[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	5.4904	8.105	66.384	90.43
pumps	12	10	1.03514	1.343	11.151	6.239
dogs	2	720	NA	NA	177.322	149.661
seeds	26	21	2.407	3.04244	27.261	19.306
surgical_realistic	14	12	1.26452	1.61972	15.129	8.526
magnesium	108	96	10.365	11.9575	126.788	88.491
salm	22	18	2.67227	3.29056	21.911	12.303
equiv	15	20	2.51109	3.41638	19.636	15.92
dyes	9	30	1.01046	1.33841	12.4485	12.924
stacks	6	21	1.12788	1.69432	22.663	14.607
epil	303	236	32.831	38.733	285.881	273.672
blockers	47	44	3.25156	3.71414	60.273	28.834
oxford	244	240	16.281	18.955	411.632	173.155
lsat	1006	5000	174.908	216.601	2025.34	1215.45
bones	33	422	72.877	90.169	427.904	191.95
mice	20	65	7.31125	9.40433	29.425	39.263
kidney	64	58	10.7045	16.19	69.149	69.77
leuk	18	714	20.489	26.69	208.556	196.849
leukfr	40	714	23.785	31.669	232.531	235.592