Go back to rlang::expr_deparse() except for board_url()

[juliasilge]

Addresses these user-reported issues:

• vetiver_sm_endpoint() error "object b not found" #253
• vetiver_sm_build . Error in enc2utf8(data) : argument is not a character vector  #256

The change in #241 turned out to actually break generating the plumber files for more complex boards like S3 and similar. 😩

I need to think about testing across different board types in vetiver. The pins package is tested very extensively across all the backends but vetiver does not, and here it is the code that vetiver ran that was the problem. I could probably get away with mocking vetiver_pin_read() in such tests to avoid needing to call S3 like pins CI does.

[juliasilge]

If I'm going to write some tests with mocking, I need to export new_board() from pins.

[juliasilge]

I'm going to fix this bug now, and wait on the tests since I will need to do a pins release to write the tests.