[BUG] stanc.js persisting model name & namespace between calls

[andrjohns]

Current Behavior:

After calling stanc.js once with a model name, all future calls will reuse the same initial model name:

stanc_js <- tempfile(fileext = ".js")
download.file("https://github.com/stan-dev/stanc3/releases/download/nightly/stanc.js",
              destfile = stanc_js)

qjs_ctx <- QuickJSR::JSContext$new()
qjs_ctx$source(stanc_js)

mod1 <- "data { real y_mean; } parameters { real y; } model { y ~ normal(y_mean, 1); }"

> qjs_res_1 <- qjs_ctx$call("stanc", "model_one", mod1)
> cat(qjs_res_1$result, sep = "\n")
# // Code generated by stanc v2.36.0-28-gd13e71e
# #include <stan/model/model_header.hpp>
# namespace model_one_model_namespace {
# ...

> qjs_res_2 <- qjs_ctx$call("stanc", "model_two", mod1)
> cat(qjs_res_2$result, sep = "\n")
# // Code generated by stanc v2.36.0-28-gd13e71e
# #include <stan/model/model_header.hpp>
# namespace model_one_model_namespace {
# ...

(happens with both V8 & QuickJS)

This is an issue for R packages since it leads to duplicate symbols, so I'm seeing failures like this for rstanarm:

C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_binomial.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_binomial.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here
C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_continuous.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_continuous.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here
C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_count.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_count.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here
C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_jm.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_jm.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here
C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_lm.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_lm.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here
C:\rtools44\x86_64-w64-mingw32.static.posix\bin/ld.exe: stanExports_mvmer.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_mvmer.h:29: multiple definition of `model_bernoulli_model_namespace::profiles__[abi:cxx11]'; stanExports_bernoulli.o:C:\Users\Andrew\Git\rstanarm\src/stanExports_bernoulli.h:29: first defined here

[WardBrian]

This was introduced in #1477 and should be an easy fix