test: property tests for expiry arithmetic (grant, extend, renew, subscribe) + fix main build

[adenueltech]

Closes #108

Property tests

New expiry_props test modules (proptest, 64 cases each) check every expiry rule against a plain-integer model instead of hand-picked examples.

access-lease (contracts/access-lease/src/expiry_props.rs)

• grant_lease sets expires_at = now + duration exactly, or returns InvalidDuration on u32 overflow and stores nothing.
• A lease is valid on every ledger before expires_at and invalid from expires_at on.
• extend_lease adds to max(expires_at, now), so an active lease keeps its remaining time and an expired one restarts. The result is always later than both. Overflow is rejected and the stored lease is left unchanged.
• Consecutive extensions accumulate exactly.
• Re-granting returns AlreadyActive while the lease is active; after expiry it restarts from now.
• Zero-length grants and extensions are always rejected.

subscription (contracts/subscription/src/expiry_props.rs)

• subscribe ends exactly one CYCLE after now.
• A subscription is active strictly before current_period_end.
• renew extends from max(current_period_end, now), increments total_renewals and keeps started_at.
• k early renewals add exactly k cycles.
• After cancel, access lasts until the period end and renew returns Cancelled. Re-subscribing carries over the remaining paid time, or restarts from now after it lapses.
• A duplicate subscribe while active returns AlreadySubbed and leaves the subscription unchanged.

The tests set a long minimum entry TTL on the test ledger, so time can move across several full cycles without storage being archived. The subscription Overflow branch isn't exercised: it needs a ledger within one cycle of u32::MAX, where the host's own TTL arithmetic fails first. That's noted in the test.

Fixes needed to get main building

CI on main has failed on every run since Oct 16, and the workspace didn't compile, so no tests could run. The minimal fixes, each from conflicting merges:

Area	Problem	Fix
access-lease grant_lease	Two merged bodies (Ok(lease) followed by another expression), the parse error CI reports	Delegate to the existing grant_lease_internal
all contracts	use common::{BUMP, BUMP_THRESH, DAY} clashed with each crate's own constants. common::DAY is in seconds, and its BUMP_THRESH > BUMP	Keep the original per-crate ledger-based constants
version fns	common::get_version/is_compatible are u32-based and matched none of the three call sites	Restore per-contract get_version/is_compatible (last-green behaviour)
subscription require_admin	Called common::require_admin with a DataKey	Load the admin and call it correctly
common crate	Pinned soroban-sdk = "20.0.0" (workspace is 29), not a workspace member, missing from Cargo.lock (breaks --locked)	Use the workspace SDK, add to members and lockfile
vault-registry	String::from_bytes given &Bytes	Pass the byte slice
vault-registry is_compatible	The #83 test expects "0.1." and "0.1.2.3" to be rejected, but they were accepted	Also require a non-empty, numeric patch component
subscription events	subscribe/renew emitted a map, but docs and tests specify the tuple (current_period_end, price, payment_reference)	data_format = "vec"
tests	Old ContractEvents API (len/get_unchecked), removed transfer_ownership, old 2-arg list, upgrade to a never-uploaded hash, a 32-vs-33 length typo, an empty-metadata proptest generator, a stale upgrade fixture	Ported to soroban-sdk 29 and the two-step transfer, passed &false, &None to list (old behaviour), uploaded real WASM, fixed the typo and generator, regenerated the fixture with make fixture steps (stellar-cli 27.0.0)
lint	clippy len_zero, cargo fmt	Fixed

How I tested (same steps as CI)

• cargo fmt --all -- --check: OK
• cargo clippy --workspace --all-targets --locked -- -D warnings: OK
• RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps --locked: OK
• cargo test --locked -p vault-registry: 62 passed
• cargo test --locked -p access-lease: 34 passed (incl. 6 property tests)
• cargo test --locked -p subscription: 14 passed (incl. 6 property tests)
• Gas report test: OK
• stellar contract build: all 3 contracts build

Note: the stricter vault-registry::is_compatible also rejects strings that aren't X.Y.Z. #144 (the docs PR for #115) lists the cases that return false, and I'll add this one there.

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