feat: Implement dynamic L2-to-L1 log tree depth

[slowli]

What ❔

Implements dynamic depth of the in-memory L2-to-L1 log Merkle tree. Previously, this tree always had 512 items (if necessary, additional zero items were added at the end). With these changes, the tree has at least 512 items (with padding); the actual number of items is max(512, items.len().next_power_of_two()). This makes the change backward-compatible without needing any logic tied to L1 batch number etc.

Why ❔

We want to allow larger Merkle tree depths than previously.

Checklist

• PR title corresponds to the body of PR (we generate changelog entries from PRs).
• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• Code has been formatted via zk fmt and zk lint.

[codecov]

Codecov Report

Attention: 49 lines in your changes are missing coverage. Please review.

Comparison is base (8df1127) 31.57% compared to head (6291e07) 31.58%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #126      +/-   ##
==========================================
+ Coverage   31.57%   31.58%   +0.01%     
==========================================
  Files         477      477              
  Lines       25429    25432       +3     
==========================================
+ Hits         8028     8032       +4     
+ Misses      17401    17400       -1     

Files	Coverage Δ
core/lib/types/src/commitment.rs	73.19% <ø> (ø)
core/lib/types/src/l2_to_l1_log.rs	100.00% <ø> (ø)
core/lib/mini_merkle_tree/src/lib.rs	63.63% <46.15%> (-5.60%)	⬇️
.../zksync_core/src/api_server/web3/namespaces/zks.rs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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