test(vault): add DepositTooSmall and WithdrawalTooSmall tests

[Onyii1234]

Summary

• Added deposit_too_small_after_share_price_inflation: seeds the vault with a 1-stroop deposit, then mints 100 USDC directly to the adapter to inflate total_assets without touching total_shares. The share price rises to ~10^9 stroops per share, so a subsequent 1-stroop deposit yields shares_to_mint = 1 * (1 + 1000) / (1_000_000_001 + 1000) = 0. Asserts try_deposit returns Err(Ok(ContractError::DepositTooSmall)).
• Added withdrawal_too_small_when_usdc_drained_from_adapter: deposits 100 USDC (1_000_000_000 stroops), then transfers all but 1 stroop of USDC away from the adapter (valid under mock_all_auths). With the adapter's USDC balance at 1 stroop but 1_000_000_000 adapter shares outstanding, burning 2 vault shares yields usdc_out = 2 * 1 / 1_000_000_000 = 0. Asserts try_withdraw returns Err(Ok(ContractError::WithdrawalTooSmall)).

Both tests exercise the share-price math paths that were previously the only error variants in lib.rs without dedicated test coverage. The existing test suite covers ZeroAmount, InsufficientShares, NoSharesOutstanding, AlreadyInitialized, and AdapterSwapUnsafe; these two complete coverage of the full ContractError enum's exercisable paths.

Test plan

• pnpm lint && pnpm typecheck && pnpm test pass locally
• cargo test -p meridian-vault passes with both new tests present (verified math manually — see comments in each test for the exact rounding calculation)
• cargo fmt --all -- --check passes (file ends with a trailing newline; no formatting changes introduced)

Closes #434

[vercel]

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[Onyii1234]

done sir you should please merge pr
i have a created a seprate pr for the both issue

[collinsezedike]

Fixed the PR title myself: test(vault): add DepositTooSmall and WithdrawalTooSmall tests.

One thing left that needs your push: Commit Messages is still failing, your commit header is 75 characters, over the 72-character limit. Please read CONTRIBUTING.md's commit message convention section and shorten it to match the title above, then push.

Both new tests are correct otherwise, I ran them myself (cargo test -p meridian-vault, 34/34 pass including these two), and the rounding math in your comments checks out exactly.