Move toolchain related functions to their own file in cargo-build-sbf

[LucasSte]

Problem

As suggested by @febo, I was changing the Solana toolchain name to 1.84.1-spbf-solana-v1.50 (<rust_version>-sbpf-solana-<platform_tools_version>), but I found that the file is very confusing since the toolchain functions are intertwined with the compilation steps.

Summary of Changes

This PR has no functional change. It puts the toolchain related functions into their own file.

[febo]

I was changing the Solana toolchain name to 1.84.1-solana-v1.50 (<rust_version>-solana-<platform_tools_version>)

I think we agreed on <rust_version>-sbpf-solana-<platform_tools_version> right?

[LucasSte]

I was changing the Solana toolchain name to 1.84.1-solana-v1.50 (<rust_version>-solana-<platform_tools_version>)

I think we agreed on <rust_version>-sbpf-solana-<platform_tools_version> right?

Oh yes. I should have checked our conversation before typing the summary. My memory failed me.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.2%. Comparing base (4807a7a) to head (494b290).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6947   +/-   ##
=======================================
  Coverage    83.2%    83.2%           
=======================================
  Files         856      856           
  Lines      376390   376390           
=======================================
+ Hits       313281   313311   +30     
+ Misses      63109    63079   -30     

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[joncinque]

I didn't take a close look at the logic, but the refactor makes sense to me!