docs(blockstm): fix comments and documentation

[heksan-ui]

Description

• Use "zero value" instead of "nil" for generic type comments (V can be any type, not just pointer)
• Fix inaccurate return value description for estimate case in Read()
• Fix typo: "closing" → "closest" in mvdata.go
• Add missing SUSPENDED status to txnStatus comment
• Replace fragile line number reference with explicit entry.Lock() in scheduler.go
• Minor punctuation fixes

[aljo242]

requesting small change

[heksan-ui]

requesting small change

ready for review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.50%. Comparing base (fd82917) to head (1e242e8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25721      +/-   ##
==========================================
+ Coverage   70.26%   70.50%   +0.24%     
==========================================
  Files         835      835              
  Lines       54361    54361              
==========================================
+ Hits        38196    38328     +132     
+ Misses      16165    16033     -132     

Files with missing lines	Coverage Δ
blockstm/memdb.go	97.77% <ø> (ø)
blockstm/mvdata.go	97.00% <ø> (ø)
blockstm/mvview.go	86.40% <ø> (ø)
blockstm/scheduler.go	94.56% <ø> (ø)

... and 4 files with indirect coverage changes

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