fix: preserve emoji ZWJ sequences through YAML↔HCL roundtrip

[jccguimaraes]

hclwrite escapes U+200D (ZWJ, category Cf) via unicode.IsPrint, and
yaml.v3's is_printable misses 4-byte UTF-8, causing supplementary-plane
emoji to be re-escaped as \UXXXXXXXX on the return trip.

Post-process HCL and YAML output at each generation boundary with
unescapeHCLUnicode / unescapeYAMLUnicode, restoring raw UTF-8 for
codepoints ≥ U+00A0. Adds TestEmojiRoundtripStability to provider/github.

[github-actions]

Go test coverage: 64.8% for commit 5f2725f

⚠️ 1 of 19 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       |    62.7%
+ github.com/yldio/cinzel/internal/maputil         |    93.3%
+ github.com/yldio/cinzel/internal/naming          |    93.1%
+ github.com/yldio/cinzel/internal/pin             |    58.0%
- github.com/yldio/cinzel/internal/test            |     0.0%
+ github.com/yldio/cinzel/internal/yamlwriter      |    88.9%
+ github.com/yldio/cinzel/provider/github          |    69.0%
+ github.com/yldio/cinzel/provider/github/action   |    82.1%
+ github.com/yldio/cinzel/provider/github/job      |    92.6%
+ github.com/yldio/cinzel/provider/github/step     |    69.3%
+ github.com/yldio/cinzel/provider/github/workflow |    85.6%
+ github.com/yldio/cinzel/provider/gitlab          |    63.5%