types/Coin: compile and reuse Regexps to reduce massive RAM+CPU burn

[alessio]

This patch brings a client code breaking change. As such it requires a Stable Release Exception to be granted by the Stable Release Managers. @clevinson @ethanfrey

From: #7989
Closes: #7986

Co-authored-by: Federico Kunze 31522760+fedekunze@users.noreply.github.com
Co-authored-by: Alessio Treglia alessio@tendermint.com

Impact

The changes introduced in #7450 to support denoms custom validation
caused a significance performance hit due to the use of closures
instead of compiled regular expressions. As the reporter described in #7986,
this represents a security threat since many ParseCoin invocations made
concurrently could cause the client application to run out of RAM.

Test Case

The bug becomes visible by invoking ParseCoin concurrently 1000 times.
A benchmark test case is included in this PR.

Regression Potential

Regressions could manifest if the CoinDenomRegex was left publicly exposed
as any modification to it by the client would not trigger the recompilation of the
regular expressions that depend on it. The original patch addresses potential
regressions by replacing CoinDenomRegex with the accessor SetCoinDenomRegex()
in the the types package public interface.

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #8001 (72c4d1c) into launchpad/backports (5be42d9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@                 Coverage Diff                  @@
##           launchpad/backports    #8001   +/-   ##
====================================================
  Coverage                50.29%   50.30%           
====================================================
  Files                      338      338           
  Lines                    17570    17572    +2     
====================================================
+ Hits                      8837     8839    +2     
  Misses                    7940     7940           
  Partials                   793      793           

Impacted Files	Coverage Δ
types/coin.go	91.21% <100.00%> (+0.07%)	⬆️
types/dec_coin.go	77.82% <100.00%> (ø)

[odeke-em]

Thank you @alessio for working this, LGTM, but deferring to the release managers and also to others.

[jackzampolin]

Great catch!

[ethanfrey]

Since the previous change that this modifies was not part of a tagged release, and the default usage remains the same, I see no issues with this.

Ack

[alain2sf]

LGTM. @odeke-em nice example of profiling 👍🏻