Fix FailedToObtainBlockhash in case of empty slots

[syntrust]

Issue

The FailedToObtainBlockhash issue was reproduced:

INFO [03-09|14:19:15.072] Calculated a valid hash                  shard=0 block=10,414,872 timestamp=1,773,062,352 randao=8651fa..436b57 nonce=170,011 hash0=d04672..40e44a hash1=000000..8ce8a8 sampleIdxs="[2285954122 5178046772]"
...
INFO [03-09|14:19:40.388] Mining result loop get result            shard=0 block=10,414,872 nonce=170,011
...
ERROR[03-09|14:19:40.399] Estimate gas failed                      error="execution reverted: ErrorData: 0x4882d76b: StorageContract_FailedToObtainBlockhash()"

Cause

The chain head stayed as 10,414,872 for 3 slots during the block mined and tx estimated. The fix in #487 only waits for 1 slot at most.

We need the block number updates to avoid empty blockhash.

Solution

This PR replaces slot-based waiting with a channel-based synchronization that ensures mining results are only submitted after the L1 head has advanced past the mined block.

Tests

Tests done in local devnet:

Waiting for L1 head to advance in the case of an empty slot:

INFO [03-11|11:59:26.576] Calculated a valid hash                  shard=37 block=10,424,641 timestamp=1,773,201,564 randao=3756ab..928ca0 nonce=541,929 hash0=ea0224..c03870 hash1=000001..326081 sampleIdxs="[1226864 1215777]"
...
INFO [03-11|11:59:40.490] Mining result loop get result            shard=37 block=10,424,641 nonce=541,929
INFO [03-11|11:59:40.490] L1 head not advanced since mined block, keep waiting mined=10,424,641 latest=10,424,641
INFO [03-11|11:59:40.490] Waiting for L1 head to advance           mined=10,424,641
INFO [03-11|11:59:49.055] headUpdateCh updated                     new=10,424,642
INFO [03-11|11:59:49.055] L1 head advanced since mined block       mined=10,424,641 latest=10,424,642
INFO [03-11|11:59:49.740] Composed calldata   ...                    

Normal case:

INFO [03-11|14:13:19.923] Calculated a valid hash                  shard=37 block=10,425,204 timestamp=1,773,209,592 randao=0d1b1f..4e2cb9 nonce=482,820 hash0=735e4e..03afb1 hash1=000001..b2a4e3 sampleIdxs="[1224625 1241249]"
...
INFO [03-11|14:13:36.915] Mining result loop get result            shard=37 block=10,425,204 nonce=482,820
INFO [03-11|14:13:36.915] L1 head advanced since mined block       mined=10,425,204 latest=10,425,205
INFO [03-11|14:13:38.683] Composed calldata                        ...