Harden GenerationGuide runtime validation

[christopherkarani]

Summary

This PR addresses a production safety gap in Conduit’s public generation-guide API by removing process-terminating preconditions from runtime-facing guide builders and replacing them with safe no-op behavior.

Problem

Several public guide constructors used precondition(...) on values that may originate from dynamic runtime paths (including user/config-driven inputs):

• GenerationGuide<String>.anyOf(_:) with empty arrays
• GenerationGuide<[Element]>.minimumCount(_:) with negative values
• GenerationGuide<[Element]>.maximumCount(_:) with negative values
• GenerationGuide<[Element]>.count(_:) for negative exact counts
• GenerationGuide<[Element]>.count(_:) for ranges with negative lower bounds

In production apps, hitting these branches terminates the process.

Changes

• Replaced precondition traps with guard-based safe fallback returning .unsupported (no-op constraint).
• Added regression tests in GenerationGuideValidationTests proving:
  • empty anyOf guide degrades to no-op (no enum emitted)
  • negative array count guides degrade to no-op (no min/max items emitted)

Why this design

• Invalid guide inputs should not crash host applications.
• .unsupported already exists as an intentional no-op constraint path and integrates cleanly with schema generation.
• This keeps API compatibility and prevents runtime termination while preserving deterministic schema behavior for valid guides.

Verification

• swift test --filter GenerationGuideValidationTests
• swift test
• swift build

All passed locally.

[christopherkarani]

Closing as superseded. The GenerationGuide runtime validation fix was already landed via PR #59, and this branch is now stale/conflicting with no remaining unique merge value.