feat(plan): preserve literal numeric precision via raw bytes

[tdakkota]

Summary

Closes #4. Literal dedup was already precise (raw-bytes comparison via internal/jsonequal), but the plan output still lost precision: plan.LiteralCase.Value carries only the decoded float64, so integers past 2^53 and exact decimals were lossy for a backend emitting literals.

frontend.Value.Raw → ir.Literal.Raw were already preserved; this threads the raw bytes the last mile into the plan.

Changes

• plan.LiteralCase gains Raw []byte — the exact JSON source bytes (nil for synthesized literals, where Value stays authoritative). This is the single lossy plan-output surface (verified: no Representation carries a const/enum value, and there are no Default/Example fields in plan/).
• Threaded Raw through the planner's intermediate discCase and all six construction sites: literalCases, propertyDispatchCases, buildLiteralDispatch, buildPropertyDispatch, and both single-const paths in representation.go (buildScalar, buildLiteral). Both LiteralDispatch.Cases and PropertyDispatch.Cases now carry it.

Tests

Three planner tests using 9007199254740993 (2^53 + 1, not float64-representable), covering the bare-const path, the union/discCase path, and numeric property-dispatch cases — each asserts Raw holds the exact bytes.

Out of scope

The dump renderer (internal/dump/plan.go) still prints the decoded Value; left unchanged to keep this surgical (the plan struct is the backend contract, the dump is a debug view). Easy follow-up if raw output in dumps is wanted.

Verification

• go build ./..., go test ./... (incl. conformance), golangci-lint run ./... → 0 issues

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.43%. Comparing base (cdebc6a) to head (3a6bf52).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   75.54%   75.43%   -0.12%     
==========================================
  Files          42       42              
  Lines        3051     3143      +92     
==========================================
+ Hits         2305     2371      +66     
- Misses        613      629      +16     
- Partials      133      143      +10     

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