feat: wasm module hot reload

[zu1k]

What this PR does:

Let Layotto monitor whether the .wasm file has changed, and reload the .wasm file if there is a change.
Achieve the effect of dynamically replacing .wasm at runtime

Which issue(s) this PR fixes:

Fixes #165

Special notes for your reviewer:

I'm using https://github.com/fsnotify/fsnotify to monitor whether the specified .wasm file has changed. However I found events may be lost in some cases for the principle of fsnotify. The fsnotify is based on the file system and OS features. For example, on GNU/Linux, inotify is taking the info from the inode of the file, and not the file name. If a file is deleted and it is created again, it may have a different inode. I'm trying to watch its parent directory to deal with this case.

When using mv to overwrite the wasm file, it will remove the file first, then rename the origin file. In this case, fsnotify will lost the monitor when got remove event, resulting in subsequent failure to continue hot loading. We won't have this problem with cp. I'm trying to solve this problem by rewatching the file when the event is remove and file still exists.

What's more, I found that mosn encapsulates wasmer but doesn't provide the ability to reload a wasm module, so currently I reload by uninstalling first and then adding, I don't think this is a good way to do it, if possible I would like someone to expose the method by create a PR for mosn.

Does this PR introduce a user-facing change?:

NONE

[mosn-community-bot]

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[zu1k]

I'm trying to create a PR for mosn to provide the ability to reload a wasm plugin. See mosn/mosn#1741 for more details.

If the PR merged, we can use a more convenient method to achieve wasm reload, see zu1k@e26d11b for the latest changes.

[codecov-commenter]

Codecov Report

Merging #168 (b12f055) into main (77e0a4b) will decrease coverage by 1.85%.
The diff coverage is 8.64%.

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
- Coverage   60.24%   58.38%   -1.86%     
==========================================
  Files          49       50       +1     
  Lines        2065     2146      +81     
==========================================
+ Hits         1244     1253       +9     
- Misses        700      772      +72     
  Partials      121      121              

Impacted Files	Coverage Δ
pkg/wasm/factory.go	2.17% <0.00%> (-0.03%)	⬇️
pkg/wasm/watcher.go	8.75% <8.75%> (ø)
...kg/filter/network/tcpcopy/persistence/work_pool.go	90.19% <0.00%> (+3.92%)	⬆️

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[seeflood]

Cool,thanks for your contribution!
I did not expect the fsnotify library to have such flaws...

[zhenjunMa]

@zu1k thank you for your contribute!