Document the storage `DataKey` map and additive-key policy in `docs/escrow-data-model.md`

[mikewheeleer]

Description

DataKey defines 20+ variants spanning instance and persistent storage with subtle defaults (unwrap_or) and the ADR-007 additive-key policy. Produce an authoritative data-model reference describing each key, its storage tier (instance vs persistent), value type, default-on-absence behavior, and which SCHEMA_VERSION introduced it.

Requirements and context

• Scoped to the LiquiFact escrow Soroban contract.
• Table every DataKey variant with: storage tier, value type, default when absent, schema version added (cross-ref the changelog in lib.rs).
• Explicitly note which keys are per-address (e.g. InvestorContribution, InvestorAllowlisted) and which use persistent().
• Document the additive-vs-breaking rules from ADR-007 and the migrate redeploy policy.
• Invariant: documentation must match the DataKey enum and its rustdoc in lib.rs.
• Must be accurate, reviewed, and aligned with code.

Suggested execution

• Fork the repo and create a branch:
  • git checkout -b docs/data-model-keys
• Implement changes:
  • escrow/src/lib.rs
  • Tests: escrow/src/tests/init.rs
  • Docs: docs/escrow-data-model.md
  • Include rustdoc/NatSpec-style doc comments on public functions
  • Validate security assumptions (auth, overflow, storage TTL, double-spend)

Test and commit

• Run tests: cargo test
• Cover edge cases (zero amounts, overflow, unauthorized callers, double-spend, state-machine misuse)
• Include test output and security notes in the PR

Example commit message

docs(escrow): authoritative DataKey storage reference

Guidelines

• Minimum 95% test coverage on new/changed code
• Clear documentation
• Timeframe: 96 hours from assignment

[Vvictor-commits]

@Vvictor-commits has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

please assign this issue to me

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[drips-wave]

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