fix(gitlab): write nested maps as blocks only where the schema declares one

[jccguimaraes]

Closes #23.

writeGenericMap decided block-vs-attribute from the value's shape — any nested map became an HCL block. The schema in provider/gitlab/config.go declares several of those keys as hcl.Expression, so the output did not parse:

• cache.key as a map (the key: files: form)
• services[].variables
• default.retry as a map
• include.inputs (CI components)

each failing with Blocks of type "..." are not expected here.

The writer now reads block names off the hcl tags and carries the matching schema down as it descends, so the decision comes from the same place the parser's does. artifacts.reports still writes as a block — that is what its hcl:",remain" body declares. A top-level key outside the schema keeps the permissive behaviour, since there is nothing to check it against.

Templates had the mirror bug: their bodies went through the generic writer too, which wrote rules as an attribute (An argument named "rules" is not expected here) because the value was a list rather than a map. A template body is a job body, so it now goes through writeJobBlock, which already handles rule, cache, artifacts and service.

Five of the six subtests verified to fail against the previous code. The sixth (artifacts.reports) passes both ways on purpose — it guards against over-correcting the keys that were already right.

[github-actions]

Go test coverage: 66.6% for commit 9e14eea

⚠️ 1 of 20 packages have zero coverage.

• github.com/yldio/cinzel/internal/test

View coverage for all packages

# Package Name                                     | Coverage
+ github.com/yldio/cinzel                          |    80.0%
+ github.com/yldio/cinzel/internal/ai              |    46.8%
+ github.com/yldio/cinzel/internal/cinzelerror     |    18.2%
+ github.com/yldio/cinzel/internal/command         |    39.5%
+ github.com/yldio/cinzel/internal/filereader      |    50.0%
+ github.com/yldio/cinzel/internal/filewriter      |    88.9%
+ github.com/yldio/cinzel/internal/fsutil          |    68.0%
+ github.com/yldio/cinzel/internal/hclparser       |    63.7%
+ github.com/yldio/cinzel/internal/maputil         |    93.3%
+ github.com/yldio/cinzel/internal/naming          |    93.1%
+ github.com/yldio/cinzel/internal/pin             |    54.8%
- github.com/yldio/cinzel/internal/test            |     0.0%
+ github.com/yldio/cinzel/internal/yamldoc         |    77.4%
+ github.com/yldio/cinzel/internal/yamlwriter      |    88.9%
+ github.com/yldio/cinzel/provider/github          |    70.9%
+ github.com/yldio/cinzel/provider/github/action   |    76.9%
+ github.com/yldio/cinzel/provider/github/job      |    95.0%
+ github.com/yldio/cinzel/provider/github/step     |    71.7%
+ github.com/yldio/cinzel/provider/github/workflow |    85.1%
+ github.com/yldio/cinzel/provider/gitlab          |    67.9%