fix(circleci_project): in-place updates no longer cascade replacement; fix pr_only_branch_overrides quoting

[james-crowley]

What this fixes

Two bugs in circleci_project that combine to make in-place updates unsafe.

1. Cascading replacement on benign edits

Changing any field on a circleci_project (e.g. auto_cancel_builds = false) plans as a destructive cascade:

Plan: 4 to add, 6 to change, 4 to destroy.

# circleci_context_restriction.X            must be replaced
# circleci_project_environment_variable.Y   must be replaced
# circleci_webhook.Z                        must be replaced

Any resource referencing circleci_project.X.id or .slug (context restrictions, project env vars, webhooks scoped to the project) gets destroyed and recreated. Project env vars carry secrets, so this silently drops customer secrets on apply.

Cause: Computed attributes including id and slug had no UseStateForUnknown plan modifier, so the framework marked them Unknown during plan whenever any other field changed. Dependents whose RequiresReplace fields reference the project then had to replace.

Fix: add UseStateForUnknown to all Computed attributes. Same pattern is already used in runner_resource_class_resource.go in this repo.

2. pr_only_branch_overrides elements get double-quoted (Fixes #59)

pr_only_branch_overrides = ["main"]

…fails apply with:

Error: Provider produced inconsistent result after apply
.pr_only_branch_overrides[0]: was cty.StringVal("main"),
but now cty.StringVal("\"main\"").

Cause: Create and Update extract list elements via branch.String(), which returns the Terraform-syntax representation (literally "main" including the quotes). The quoted strings were sent to the API and stored.

Fix: use elem.(types.String).ValueString() instead — the same pattern used for individual string attributes in this provider.

#61 proposed the same extraction fix bundled with a ListAttribute → SetAttribute schema change. This PR keeps the existing list type to avoid breaking existing HCL; the type-shape decision can be a separate follow-up.

Why both in one PR

Fix 1 alone exposes Fix 2: removing the cascade means Update actually runs (it didn't before, because every change destroyed and recreated), which immediately trips the quoting bug. Shipping Fix 1 without Fix 2 just moves the failure from "destructive plan" to "apply error".

Testing

Tested locally against a CircleCI standalone organization with a project, two project env vars, a context restriction, and a webhook.

Before: toggling auto_cancel_builds plans as 4 add / 6 change / 4 destroy. Forcing past that hits the pr_only_branch_overrides 400.

After: same toggle plans as 0 add / 1 change / 0 destroy, applies clean, re-plan reports No changes. Setting pr_only_branch_overrides = ["main", "develop"] and applying stores the values verbatim with no embedded quotes.

Migration note

Existing projects whose API state has the quoted form stored (["\"main\""]) will continue to read that way until cleaned up. Setting pr_only_branch_overrides explicitly in HCL and applying once overwrites the API state via the corrected Update path.

Closes #59.