Remove redundant bounds check from getBlock and getBlockTime

[steviez]

Problem

See #33859 for some additional details but the TLDR is:

• The current logic in rpc.rs looks up min/max roots from the Blockstore to perform bounds check for the sake of error reporting
• Looking up these roots is currently expensive as it is done by constructing an iterator
• Regardless of the overhead of looking up min/max roots, some of these checks are repetitive

Summary of Changes

Remove / condense code to avoid repeating checks that have already occurred. Namely,

• Blockstore::is_skipped(), which was called by these two RPC methods, has been removed as it was redundant
  • This avoids the overhead of (2) rocksdb iterators
• Rename check_blockstore_root() ==> check_blockstore_bounds() and add a bunch of comments about the handling of Blockstore errors at the RPC level

[steviez]

@CriesofCarrots - This doesn't compile yet, but I think you should be able to get the gist. Hopefully my comments inline help illustrate why I think the call to Blockstore::is_skipped() is redundant. This RPC helper is the only caller of Blockstore::is_skipped(), so we can hypothetically remove it as part of this PR too.

One downside is that this function is no longer self contained as it relies on checks from the actual blockstore fetch. This is obviously not ideal, but saving the creation of the two extra iterators is pretty big I think.

Also, thinking on it more, we likely don't even need to check for greater than max root in the helper; we explicitly check for lower than latest root at the top level when we decide to call get_rooted_block_time()

[codecov]

Codecov Report

Merging #33901 (4bd6503) into master (70d97d3) will increase coverage by 0.0%.
Report is 3 commits behind head on master.
The diff coverage is 41.6%.

@@           Coverage Diff           @@
##           master   #33901   +/-   ##
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  Coverage    81.9%    81.9%           
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  Files         811      811           
  Lines      219332   219318   -14     
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+ Hits       179703   179707    +4     
+ Misses      39629    39611   -18