test: add Go unit tests for the codegen, idnaref, and ucd packages

[OmarAlJarrah]

The Go code under tools/ has no tests — go test ./... reports "no test files" for every package. These packages are load-bearing:

• tools/internal/codegen emits the committed Kotlin lookup tables and conformance fixtures.
• tools/internal/ucd parses the Unicode Character Database.
• tools/internal/idnaref is the reference implementation whose output derives the IDNA known-failures baseline that the Kotlin conformance suite ratchets against.

A bug in any of them can silently corrupt generated data or the derived baseline. Add Go unit tests, for example:

• ucd: parsing of code-point ranges and First/Last blocks, hex-scalar fields, and the merged mapping / validity / NFC / Bidi tables over small fixtures.
• idnaref: targeted ToASCII cases (mapping, NFC, Punycode round-trips, ContextJ, CheckBidi, decoded-A-label re-validation), plus spot-checks that its verdicts match the Kotlin runtime's expected behaviour.
• codegen: the chunking / escaping helpers, the JSON lone-surrogate decoder, and byte-stable output from each generator.

Wire go test ./... into the contributor workflow (and into CI once it exists).

[AhmadAL-Quraan]

Hey Omar,
If there is no one assigned to this, I would love working on it
I will start adding/doing unit tests on the files you mentioned, using testing package
I don't know if there is a specific patterns that you would suggest to test based on, but I will use :

Table-driven tests with t.Run, for the ucd parsing cases and idnaref ToASCII cases
Golden files (testdata/ + an -update flag) , for the "byte-stable output" requirement on codegen

Also, do you want this as a one PR or split per package ?

[OmarAlJarrah]

Hi @AhmadAL-Quraan, assigning this to you.

[OmarAlJarrah]

@AhmadAL-Quraan
For the pattern, please check our styleguide.
It would be better if you split this into multiple PRs. We do not expect a 100% coverage, adding any tests for now is good enough.

[AhmadAL-Quraan]

@OmarAlJarrah
Hey Omar, Please check the unit tests for /ucd