fix(sdk): preserve intrinsic stubs under LTO

[greenhat]

Close #1089

LTO can see through the Rust unreachable stubs used to carry Miden intrinsic signatures and rewrite callers as if those stubs were the real implementations. That breaks frontend lowering because the final wasm no longer reliably preserves the call ABI the linker-stub recognizer expects.

Mark SDK intrinsic declarations as weak externs, keep stub bodies uninlined and unoptimized, and force the tiny stub archives into linked wasm with whole-archive. This keeps the stubs available for signature recognition without letting LTO propagate their unreachable bodies into callers.

MAST Sizes

Values are from tests/integration/src/rust_masm_tests/examples.rs.

Package	next	current	Delta	Reduction
examples/basic-wallet	35,906	18,893	-17,013	47.38%
examples/basic-wallet-tx-script	56,437	17,475	-38,962	69.04%
examples/p2id-note	53,082	21,396	-31,686	59.69%
examples/p2ide-note	62,672	24,878	-37,794	60.30%
Total	208,097	82,642	-125,455	60.29%

Mockchain Cycle Counts

Values are from the tests/integration-network/src/mockchain expectations.

Test measurement	next	current	Delta	Reduction
basic_wallet::test_basic_wallet_p2id mint note cycles	20,072	7,275	-12,797	63.76%
basic_wallet::test_basic_wallet_p2id tx script processing cycles	26,217	6,723	-19,494	74.36%
basic_wallet::test_basic_wallet_p2id Bob note cycles	20,072	7,275	-12,797	63.76%
basic_wallet::test_basic_wallet_p2ide Bob note cycles	21,211	7,721	-13,490	63.60%
basic_wallet::test_basic_wallet_p2ide_reclaim reclaim note cycles	22,871	8,280	-14,591	63.80%
counter_contract::test_counter_contract note cycles	49,505	10,474	-39,031	78.84%
counter_contract_no_auth::test_counter_contract_no_auth auth procedure cycles	1,803	1,778	-25	1.39%
counter_contract_no_auth::test_counter_contract_no_auth note cycles	49,505	10,474	-39,031	78.84%
counter_contract_rust_auth::test_counter_contract_rust_auth_blocks_unauthorized_note_creation auth procedure cycles	86,895	74,561	-12,334	14.19%

[bitwalker]

@greenhat If you rebase this on next, I'll get it merged today

[greenhat]

@greenhat If you rebase this on next, I'll get it merged today

Rebased.