load contract bytes at runtime in deploy_native_contracts

[noot]

using the drk crate as a dep in an external repo led to these compilation errors:

error: couldn't read `/home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/../contract/money/darkfi_money_contract.wasm`: No such file or directory (os error 2)
  --> /home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/utils.rs:57:13
   |
57 |             include_bytes!("../contract/money/darkfi_money_contract.wasm").to_vec(),
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `include_bytes` (in Nightly builds, run with -Z macro-backtrace for more info)

error: couldn't read `/home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/../contract/dao/darkfi_dao_contract.wasm`: No such file or directory (os error 2)
  --> /home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/utils.rs:63:13
   |
63 |             include_bytes!("../contract/dao/darkfi_dao_contract.wasm").to_vec(),
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `include_bytes` (in Nightly builds, run with -Z macro-backtrace for more info)

error: couldn't read `/home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/../contract/deployooor/darkfi_deployooor_contract.wasm`: No such file or directory (os error 2)
  --> /home/e/.cargo/git/checkouts/darkfi-a258e322f5e79994/bfcd383/src/validator/utils.rs:69:13
   |
69 |             include_bytes!("../contract/deployooor/darkfi_deployooor_contract.wasm").to_vec(),
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `include_bytes` (in Nightly builds, run with -Z macro-backtrace for more info)

the relative path used in include_bytes turned into /src/validator/../contract/money/darkfi_money_contract.wasm when darkfi is used as a lib, which is not a valid path.

this PR fixes the issue by loading the wasm bytes at runtime, using CARGO_MANIFEST_DIR to get a nonrelative path.

this was tested using a patch as follows + make clippy:

[patch."https://github.com/darkrenaissance/darkfi"]
darkfi = { git = "https://github.com/noot/darkfi", branch = "fix-include-bytes" }