Support fetching-then-parsing-with-key

[rtyley]

This is motivated by fixing Prout's flakey integration tests:

• Fix flakey tests where scan fails to find & label Test PR prout#146 - Prout makes extensive use of the GitHub API, and its integration test suite involves creating little test repos as test fixtures. Unfortunately, creation of these fixtures would frequently & unpredictably fail.
• Fix creation of Test repos: replace OkHttp's ETag support with com.gu.etag-caching , adopt Cats Effect (IO) rtyley/play-git-hub#18 - the failures were partly caused by bad caching behaviour in OkHttp, which occasionally was not refreshing the cached responses of conditional requests to the GitHub API. To fix this, play-git-hub has switched to use our own etag-caching library instead.

The one blocker for play-git-hub using our own etag-caching library is that the library currently only provides the response to the parser. Yet GitHub API responses do not contain a discriminator which makes it easy to work out what the correct parser is to use - is the response a Repo, a PullRequest or what!? Therefore we need etag-caching to support parser functions that require knowledge of the key, as well as the raw response.

Changes

• Add a new fetching.thenParsingWithKey() syntax to complement the fetching.thenParsing() method of instantiating a Loading instance - which passes the key, as well as the raw response, to the parser.
• Drop the Loading.by(fetching)(parser) syntax for instantiating a Loading instance, in favour of the alternative fetching.thenParsing(parser) syntax (which previously delegated to Loading.by(fetching)(parser)). We don't need two syntaxes for doing the same thing, and the fetching.thenParsing(parser) syntax seems more convenient. I definitely didn't want to have the 2x2 matrix of methods covering with/without-key * located-on-Loading/Fetching.

[gu-scala-library-release]

@rtyley has published a preview version of this PR with release workflow run #242, based on commit 0c1dbde:

11.0.0-PREVIEW.support-fetching-then-parsing-with-key.2025-09-03T1555.0c1dbdea

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gh workflow run release.yml --ref support-fetching-then-parsing-with-key

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Click 'Run workflow' in the GitHub UI, leaving the branch as the default, or use the GitHub CLI command:

gh workflow run release.yml

[gu-scala-library-release]

@rtyley has published a preview version of this PR with release workflow run #244, based on commit 32fe2e2:

11.0.0-PREVIEW.support-fetching-then-parsing-with-key.2025-09-04T1544.32fe2e20

Want to make another preview release?

Click 'Run workflow' in the GitHub UI, specifying the support-fetching-then-parsing-with-key branch, or use the GitHub CLI command:

gh workflow run release.yml --ref support-fetching-then-parsing-with-key

Want to make a full release after this PR is merged?

Click 'Run workflow' in the GitHub UI, leaving the branch as the default, or use the GitHub CLI command:

gh workflow run release.yml

[gu-scala-library-release]

@rtyley has published a preview version of this PR with release workflow run #245, based on commit 32fe2e2:

11.0.0-PREVIEW.support-fetching-then-parsing-with-key.2025-09-04T2020.32fe2e20

Want to make another preview release?

Click 'Run workflow' in the GitHub UI, specifying the support-fetching-then-parsing-with-key branch, or use the GitHub CLI command:

gh workflow run release.yml --ref support-fetching-then-parsing-with-key

Want to make a full release after this PR is merged?

Click 'Run workflow' in the GitHub UI, leaving the branch as the default, or use the GitHub CLI command:

gh workflow run release.yml

[gu-scala-library-release]

@rtyley has published a preview version of this PR with release workflow run #248, based on commit 3b4c706:

11.0.0-PREVIEW.support-fetching-then-parsing-with-key.2025-09-09T0923.3b4c7060

Want to make another preview release?

Click 'Run workflow' in the GitHub UI, specifying the support-fetching-then-parsing-with-key branch, or use the GitHub CLI command:

gh workflow run release.yml --ref support-fetching-then-parsing-with-key

Want to make a full release after this PR is merged?

Click 'Run workflow' in the GitHub UI, leaving the branch as the default, or use the GitHub CLI command:

gh workflow run release.yml

[gu-scala-library-release]

@rtyley has published a preview version of this PR with release workflow run #251, based on commit abf81f8:

11.0.0-PREVIEW.support-fetching-then-parsing-with-key.2025-10-10T2129.abf81f84

Want to make another preview release?

Click 'Run workflow' in the GitHub UI, specifying the support-fetching-then-parsing-with-key branch, or use the GitHub CLI command:

gh workflow run release.yml --ref support-fetching-then-parsing-with-key

Want to make a full release after this PR is merged?

Click 'Run workflow' in the GitHub UI, leaving the branch as the default, or use the GitHub CLI command:

gh workflow run release.yml