fix(storage-provider): concurrency & logic bugs in add_piece

[jmg-duarte]

Description

Fixes a BIG logic bug in the find sector logic & fixes a concurrency bug/issue in the overall process for add piece.

Blocking #733

To test, apply the following change to start_sp.sh

diff --git a/examples/start_sp.sh b/examples/start_sp.sh
index eca6231d..b1ac1e31 100755
--- a/examples/start_sp.sh
+++ b/examples/start_sp.sh
@@ -31,16 +31,16 @@ wait
 # It's a test setup based on the local verifying keys, everyone can run those extrinsics currently.
 # Each of the keys is different, because the processes are running in parallel.
 # If they were running in parallel on the same account, they'd conflict with each other on the transaction nonce.
-RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Charlie" storage-provider register "$PEER_ID" &
-RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Alice" proofs set-porep-verifying-key @2KiB.porep.vk.scale &
-RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Bob" proofs set-post-verifying-key @2KiB.post.vk.scale &
+RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Charlie" storage-provider register --post-proof 8MiB "$PEER_ID" &
+RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Alice" proofs set-porep-verifying-key @8MiB.porep.vk.scale &
+RUST_LOG=debug target/release/storagext-cli --sr25519-key "//Bob" proofs set-post-verifying-key @8MiB.post.vk.scale &
 wait
 
 echo '{
-    "seal_proof": "2KiB",
-    "post_proof": "2KiB",
-    "porep_parameters": "2KiB.porep.params",
-    "post_parameters": "2KiB.post.params",
+    "seal_proof": "8MiB",
+    "post_proof": "8MiB",
+    "porep_parameters": "8MiB.porep.params",
+    "post_parameters": "8MiB.post.params",
     "p2p_key": "@/tmp/private.pem",
     "rendezvous_point_address": "/ip4/127.0.0.1/tcp/62649",
     "sealing_configuration": {

And run examples/rpc_publish_multiple_sectors.sh with a file (for easier testing) around ~3MB

Checklist

• Have you tested this solution?
• Did you document new (or modified) APIs?

[cernicc]

Great catch