Fix a bug about blocks api paging

[anarcher]

Github Issue

Background

• /api/v1/blocks 's cursor is height cursor=12123. So this cursor should not do base64 encoding
• Remove storage.WalkOption.SkipCursor. It's an insane approach.

Solution

• PageQueryOption for base64encoding or not. Default is encoding. e.g. p, err := NewPageQuery(r, WithEncodePageCursor(false))
• Remove WalkOption.SkipCursor
• Without cursor, storage.Walk call iter.Last() or iter.First() depend on WalkOption.Reverse.

Possible Drawbacks

[codecov-io]

Codecov Report

Merging #845 into master will increase coverage by 0.04%. The diff coverage is 77.5%.

@@            Coverage Diff             @@
##           master     #845      +/-   ##
==========================================
+ Coverage   62.14%   62.19%   +0.04%     
==========================================
  Files         152      152              
  Lines       10026    10062      +36     
==========================================
+ Hits         6231     6258      +27     
- Misses       3120     3126       +6     
- Partials      675      678       +3

Flag	Coverage Δ
#integration_tests_long_term	45.34% <0%> (-0.13%)	:arrow_down:
#integration_tests_node	40.99% <0%> (-0.16%)	:arrow_down:
#unittests	51.4% <77.5%> (+0.09%)	:arrow_up:

Impacted Files	Coverage Δ
lib/node/runner/api/resource/resource.go	91.66% <ø> (ø)	:arrow_up:
lib/storage/leveldb.go	63.6% <56.25%> (-0.78%)	:arrow_down:
lib/node/runner/api/pagequery.go	85.89% <81.81%> (-1.99%)	:arrow_down:
lib/node/runner/api/blocks.go	75.47% <83.33%> (+0.47%)	:arrow_up:
lib/node/runner/node_runner.go	77.9% <0%> (+0.44%)	:arrow_up:

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[anarcher]

4cbe905 What do you think? If the next cursor is empty, don't display hal next .

[spikeekips]

@anarcher : 4cbe905 What do you think? If the next cursor is empty, don't display hal next .

In most cases for 'hal', the 'next' and 'prev' link exists with same link, not empty.

[anarcher]

@kfangw Plz review it