crit: add features to retrieve memory pages

[behouba]

The goal of this PR is to add features for collecting memory pages content.
For the now I have added GetMemPages function to retrieve the memory pages of a process. Alongside it, helper functions genMemChunk and getPage have been implemented. The core logic is derived from https://github.com/checkpoint-restore/criu/blob/criu-dev/coredump/criu_coredump/coredump.py.

It's still a work in progress, but I would like to submit it for feedback.

PTAL: @adrianreber, @rst0git

Thank you!

[codecov]

Codecov Report

Patch coverage: 78.57% and project coverage change: +1.91 🎉

Comparison is base (748b90b) 48.33% compared to head (4c337d0) 50.25%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #133      +/-   ##
==========================================
+ Coverage   48.33%   50.25%   +1.91%     
==========================================
  Files          23       24       +1     
  Lines        2435     2589     +154     
==========================================
+ Hits         1177     1301     +124     
- Misses       1084     1104      +20     
- Partials      174      184      +10     

Impacted Files	Coverage Δ
test/crit/main.go	52.20% <33.33%> (-9.34%)	⬇️
crit/mempages.go	97.24% <97.24%> (ø)

... and 1 file with indirect coverage changes

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[adrianreber]

Thanks for the PR. I am a bit unsure about the design. Returning the content of the pages as a return parameter does not sound right. For large memory areas I would expect that using pointers would be better and would hopefully require less data movement.

Nice to see tests included in the PR. You could try to also pass a couple of wrong parameters to test the error paths as well.

[behouba]

I have made a few changes to the previous implementation:

• Added a MemoryReader struct to encapsulate common and reusable data.
• Modified the GetMemPages function to accept addresses (start and end) for flexibility, enabling the retrieval of specific portions of memory (e.g., mm_arg, mm_env, pagemap addresses etc.).
• The GetMemPages function now returns a *bytes.Buffer instead of []byte.

Do you think this is a good direction for ?

[rst0git]

LGTM

[adrianreber]

Looks very good. Thanks.