Prefer is_and_then and is_ok_than over map_or

[mina86]

Option::is_and_then and Result::is_ok_then have been stabilised
in 1.70 and are slightly more concise and arguably more descriptive
than map_or.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (84f3d28) 71.88% compared to head (02b1149) 71.88%.

Files	Patch %	Lines
nearcore/src/lib.rs	0.00%	1 Missing ⚠️
...me/near-vm-runner/src/instrument/gas/validation.rs	0.00%	1 Missing ⚠️
runtime/near-vm-runner/src/prepare/prepare_v0.rs	0.00%	0 Missing and 1 partial ⚠️
runtime/near-vm-runner/src/prepare/prepare_v1.rs	0.00%	0 Missing and 1 partial ⚠️
tools/state-viewer/src/rocksdb_stats.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10408      +/-   ##
==========================================
- Coverage   71.88%   71.88%   -0.01%     
==========================================
  Files         719      719              
  Lines      144841   144837       -4     
  Branches   144841   144837       -4     
==========================================
- Hits       104122   104119       -3     
+ Misses      35957    35956       -1     
  Partials     4762     4762              

Flag	Coverage Δ
backward-compatibility	0.08% <0.00%> (ø)
db-migration	0.08% <0.00%> (ø)
genesis-check	1.25% <0.00%> (ø)
integration-tests	36.68% <50.00%> (+<0.01%)	⬆️
linux	71.43% <72.22%> (+0.01%)	⬆️
linux-nightly	71.46% <72.22%> (-0.01%)	⬇️
macos	53.68% <13.33%> (+<0.01%)	⬆️
pytests	1.48% <0.00%> (ø)
sanity-checks	1.27% <0.00%> (ø)
unittests	68.12% <72.22%> (+<0.01%)	⬆️
upgradability	0.13% <0.00%> (ø)

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[wacban]

LGTM, thanks!