Add embedded-ready SDK abstractions

[tolgahan-arikan]

Summary

• regenerate the WaaS C client from the updated generic generator
• replace process-global SDK state with caller-owned oms_wallet_sdk_t contexts
• add injectable signer, session store, and SDK-wide transport providers for embedded integrations
• make the built-in curl transport optional and propagate bounded response sizes
• update wallet transaction flow to prepare/execute/status and poll demos/CLI until executed
• add provider and embedded secure-auth simulator coverage

Verification

• cmake --build build
• ctest --test-dir build --output-on-failure
• cmake -S . -B build-no-curl -DOMS_WALLET_ENABLE_CURL_TRANSPORT=OFF -DOMS_WALLET_BUILD_DEMO=OFF -DOMS_WALLET_BUILD_CLI=OFF -DBUILD_TESTING=ON
• cmake --build build-no-curl
• ctest --test-dir build-no-curl --output-on-failure

Manual demo check

• interactive demo completed email auth, message signing, signature verification, transaction execute, and transaction status polling to executed