fix(rust): only clear config.environment in wire tests when multiple base URLs exist, fix pagination error tests

[iamnamananand996]

Description

Linear ticket: Closes

Fixes two issues in the Rust SDK generator that broke generated wire tests and pagination unit tests:

1. Wire test generator unconditionally emitted config.environment = None; for the WireMock test setup. Single-URL SDKs do not expose an environment field on ClientConfig, so the generated test failed to compile. The line is now only emitted when the SDK was generated against multiple base URLs (i.e. context.hasMultipleBaseUrls() is true).
2. Pagination error-propagation tests in the Rust base template referenced ApiError::Serialization, which is not a valid variant in the current ApiError enum, so the test file failed to compile. Switched the test fixtures to ApiError::Configuration, which is the appropriate variant for synthesizing a configuration-style error from the paginator callback.

Seed snapshots for rust-sdk fixtures (multi-url-environment, pagination, single-url-environment-default/{basic,custom-environment,full-custom}) were regenerated to reflect the above. The single-URL full-custom wire test no longer carries the unused config.environment = None; line.

Note: this branch is stacked on top of #15854 (the ruby-v2 empty-comment RuboCop fix), so that commit appears in the diff. It will drop out once #15854 lands.

Changes Made

• generators/rust/sdk/src/wire-tests/WireTestGenerator.ts: gate the config.environment = None; emission on this.context.hasMultipleBaseUrls().
• generators/rust/base/src/asIs/pagination.rs: switch the synchronous-paginator error tests from ApiError::Serialization to ApiError::Configuration.
• Regenerate seed/rust-sdk/** snapshots for the affected fixtures (pagination.rs, tests/dummy_test.rs, .fern/metadata.json).
• Updated README.md generator (if applicable)

Testing

• Unit tests added/updated
• Manual testing completed (seed snapshots regenerated; the previously failing rust-sdk wire test and pagination unit tests now compile and run).

Link to Devin session: https://app.devin.ai/sessions/2e4e587dd160400390839880a5434932
Requested by: @iamnamananand996

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SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-05-12T05:12:12Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
rust-sdk	square	153s (n=5)	156s (n=5)	154s	+1s (+0.7%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-05-12T05:12:12Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-05-12 19:35 UTC