fix: preserve TotalDeposited lifetime value across TTL expiry

[Andreas2410]

Overview

This PR fixes the silent reset of TotalDeposited(account) in the investment vault after the single persistent-entry TTL expires. The current contract only calls extend_ttl once, which caps the entry's guaranteed lifetime at roughly 518,400 ledgers (~30 days). For an investor who deposits once and never deposits again, get_portfolio reads a missing entry and silently falls back to unwrap_or(0), destroying the documented “lifetime deposited” semantics.

The fix extends the TTL window to cover the vault's intended lifetime and also renews the TTL whenever get_portfolio reads the total-deposited entry. A new regression test advances the simulated ledger past the previous expiration point and verifies the value is preserved instead of resetting to zero.

Related Issue

Changes

🗄️ Storage / TTL handling

• [MODIFY] investment_vault/src/lib.rs
  • Replaces the hard-coded 17280, 518400 TTL extension with named constants and increases the extension from 518,400 ledgers to 5,184,000 ledgers (~300 days), covering the vault's intended lifetime while keeping entries archived only after a significantly longer inactivity window.
  • Adds the same persistent-storage TTL bump in get_portfolio (lines 808-812) when reading TotalDeposited, so any active portfolio read also renews the entry and prevents expiry in live operational paths.

🧪 Regression test

• [ADD] investment_vault/src/test.rs
  • Adds test_total_deposited_survives_ttl_expiry.
  • Simulates an investor deposit, advances the ledger past the previous 518,400-ledger TTL, then calls get_portfolio and asserts total_deposited retains the original deposited amount instead of 0.

Verification Results

cargo test -p investment_vault test_total_deposited_survives_ttl_expiry
✅ 1 passed

cargo test -p investment_vault
✅ all tests passed

Acceptance Criteria	Status
TotalDeposited survives investor inactivity for the vault's intended lifetime	✅ TTL extended to 5,184,000 ledgers (~300 days) and renewed on every get_portfolio read
A test simulates ledger advancement past the current TTL and checks the value is preserved	✅ test_total_deposited_survives_ttl_expiry advances past the old 518,400-ledger point and verifies the original deposit remains

Closes #316

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