feat: SQL translator with ClickHouse dialect

[khvn26]

Contributes to Flagsmith/flagsmith#5663.

Scaffold, translator, Dialect protocol, and the first dialect (ClickHouse) for flagsmith-sql-flag-engine — sibling to flagsmith-flag-engine (Python) and flagsmith-rust-flag-engine (Rust). Translates SegmentContext predicate trees into SQL WHERE expressions.

Public API

from flagsmith_sql_flag_engine import TranslateContext, translate_segment
from flagsmith_sql_flag_engine.dialects import ClickHouseDialect

ctx = TranslateContext(
    evaluation_context={"environment": {"key": "n9fbf...3ngWhb", "name": "Production"}},
    dialect=ClickHouseDialect(),
)
where_expr = translate_segment(segment, ctx)

EnvironmentContext.key lands directly as the environment_id literal in emitted SQL — no separate integer PK.

What's included

• uv-managed Python package, src/ layout, py.typed
• Dialect protocol with ClickHouseDialect (native JSON column, typed subcolumns)
• Engine-parity harness running against a docker-compose ClickHouse — no external credentials required
• engine-test-data as a git submodule pinned to v3.7.0
• 56 translator unit tests + 599 / 3 xfailed engine-parity tests
• mypy strict, ruff, 100% line + branch coverage gate via Cobertura
• Renovate, CODEOWNERS

SnowflakeDialect follows in #9.

Operator coverage

Operator	Translatable	Notes
EQUAL, NOT_EQUAL, IN	yes
IS_SET, IS_NOT_SET	yes	trait subcolumn IS NOT NULL / IS NULL
CONTAINS, NOT_CONTAINS	yes
GREATER_THAN, LESS_THAN plus _INCLUSIVE	yes
MODULO	yes
PERCENTAGE_SPLIT	yes	inlined MD5-mod-9999; ~0.005% diverge on hash==9998
REGEX	partial	dialect-flavour gated; unsupported patterns → caller fallback
:semver-marked comparators	yes	major.minor.patch only; ignores prerelease

[github-actions]

File	Coverage		Missing
All files	100%	✅

Minimum allowed coverage is 100%

Generated by 🐒 cobertura-action against 4b87f0d

[emyller]

I've read the docs, and glanced through tests, and all the code. Honestly trusting engine test and coverage results more than my thoroughness in reviewing this, but also honestly this looks good to experiment with.