Fix selected outputs in the existing target eval cache

[jacobmichels]

A warm Tecnix target-cache hit can return dev even when the target selected out. The existing cache remembers only the .drv path—the build recipe—so importing it loses the original output selection.

This PR fixes that existing behavior. It stores {drvPath, outputName} in a versioned result payload and reconstructs the selected output with its Nix string dependency information intact. Both fields are forced while source tracking is active, including a lazy output selector that does not change the recipe. Malformed payloads, unavailable recipes, and invalid output names fall back to evaluation.

The dependency-blob version advances to 2 so older records are relearned. Those records never tracked output-selection inputs and cannot safely serve even dependency-only queries under the corrected contract. The existing SQLite filename/schema, cache eligibility, evaluator-version handling, and packaging remain unchanged.

Checks:

• Full build and the repository formatter passed.
• Isolated Linux functional-test package: 215 passed, 0 failed, 10 skipped, with sandboxing enabled.
• Tecnix builtins and gc functional suites plus nix-expr-tests: 3/3 passed.
• Regressions cover selected outputs and string contexts, dependency-only warmup, deleted recipes, malformed payloads, lazy selector changes, and rejection of legacy dependency records.

Revision identities and build metadata for future remote-cache reuse are handled separately in #58. This PR depends on #59 for SQLite in the isolated test environment. #58 is the next layer above this selected-output fix. Native stack order: #59 → #57 → #58. This PR adds no remote transport or revision-stamping machinery.