Bump MSRV to 1.70

[djc]

As discussed in #2168.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.0%. Comparing base (80771d3) to head (4f15361).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2179   +/-   ##
=====================================
  Coverage   79.0%   79.0%           
=====================================
  Files        121     121           
  Lines      20945   20945           
=====================================
+ Hits       16559   16561    +2     
+ Misses      4386    4384    -2     

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[cijothomas]

this can be skipped as otlp is already on 1.71.1

[cijothomas]

please skip this, as proto is already on 1.71.1

[cijothomas]

Thanks.
(Need a minor cleanup in changelog for proto, otlp which are already on higher version)

[lalitb]

Nit - Also update the Readme.md. Not related to this PR and to be handled separately, we need to be consistent regarding mentioning or not-mentioning msrv in Readme.md for all the otel crates.

[lalitb]

Thanks for the PR. LGTM with nit comments. There are few places for msrv patching and version pinning, which can be cleaned up now. I will raise a separate PR for that.

[cijothomas]

Merging. The nits can be fixed as part of cleanups required in the patch scipts.