feat(dpp): add documents_countable to DocumentTypeV2 for O(1) total document counts

[QuantumExplorer]

Summary

Adds two new fields to DocumentTypeV2 for O(1) document counting:

• documents_countable: bool — primary key tree uses CountTree, enabling O(1) total document count queries
• blast_syncable: bool — primary key tree uses ProvableCountTree for BLAST sync support. Implies documents_countable = true.

Changes

• DocumentTypeV2: New struct with both fields
• DocumentType enum: Added V2 variant with full match arm coverage
• Accessor traits: DocumentTypeV2Getters / DocumentTypeV2Setters
• Schema parsing: try_from_schema v2 parses both "documentsCountable" and "blastSyncable" (protocol version 12+ required)
• Drive: CountTree for countable, ProvableCountTree for blast_syncable
• Platform version: CONTRACT_VERSIONS_V4 with try_from_schema: 2, used in v12

Schema example

{
  "person": {
    "type": "object",
    "documentsCountable": true,
    "properties": { ... }
  }
}

Or with BLAST sync:

{
  "person": {
    "type": "object",
    "blastSyncable": true,
    "properties": { ... }
  }
}

NOT in this PR

Count query extensions — follow-up to PR #3435.

Test plan

• cargo check -p dpp -p drive passes
• cargo fmt --all clean
• CI

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added support for marking document types as countable, enabling O(1) total document count queries.
  • Added support for range countable documents, enabling efficient range counting operations.
  • Implemented protocol version 12 support with optimized primary key storage tree types based on document configuration.

• Chores

  • Updated schema to include new countability configuration properties.