Record requests in responses and errors

[hadley]

And polish the helpers for working with lists.

Fixes #357

[mgirlich]

Maybe resps_data() should check that all responses were successful. And I get this beauty when applying to an error:

devtools::load_all("~/GitHub/httr2/")
#> ℹ Loading httr2
reqs <- list(
  request(example_url()) |> req_template("/status/:status", status = 404),
  request("INVALID")
)
resps <- req_perform_parallel(reqs)

resps |> resps_data(\(resp) resp_body_json(resp))
#> Error in `env_has()` at httr2/R/resp-body.R:82:2:
#> ! `env` must be an environment, not `NULL`.
#> Backtrace:
#>     ▆
#>  1. └─httr2::resps_data(resps, function(resp) resp_body_json(resp))
#>  2.   ├─vctrs::list_unchop(lapply(resps, resp_data)) at httr2/R/iterate-responses.R:62:2
#>  3.   └─base::lapply(resps, resp_data)
#>  4.     └─global FUN(X[[i]], ...)
#>  5.       └─httr2::resp_body_json(resp)
#>  6.         └─rlang::env_has(env = resp$cache) at httr2/R/resp-body.R:82:2
#>  7.           └─rlang:::check_environment(env)
#>  8.             └─rlang:::stop_input_type(...)
#>  9.               └─rlang::abort(message, ..., call = call, arg = arg)

^{Created on 2023-10-27 with reprex v2.0.2}

This suggests that we should be more careful with the caching in resp_body_json() and resp_body_xml()

[hadley]

Ooops, no, that's just because check_response(resp) should come before the cache lookup, not after 😬

[mgirlich]

This looks very nice for debugging!