fix: bump MSRV to 1.71.1

[rnbguy]

Closes: #1118 Closes: #1101 Closes: #1120

Description

• Increase MSRV to 1.71.1
• Check MSRV on CI for linux and darwin
• Update README with new links
• Apply some clippy suggestions

  ---

PR author checklist:

• [x] Added changelog entry, using unclog.
• [x] Added tests.
• [x] Linked to GitHub issue.
• [ ] Updated code comments and documentation (e.g., docs/).
• [x] Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• [ ] Reviewed Files changed in the GitHub PR explorer.
• [ ] Manually tested (in case integration/unit/mock tests are absent).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 64.70588% with 78 lines in your changes are missing coverage. Please review.

Project coverage is 66.54%. Comparing base (e1f19af) to head (6161f2c).

Files	Patch %	Lines
ibc-apps/ics20-transfer/src/module.rs	9.09%	20 Missing :warning:
ibc-apps/ics721-nft-transfer/src/module.rs	9.52%	19 Missing :warning:
ibc-core/ics02-client/types/src/error.rs	0.00%	6 Missing :warning:
...ics24-host/cosmos/src/upgrade_proposal/proposal.rs	0.00%	4 Missing :warning:
ibc-clients/ics07-tendermint/types/src/error.rs	0.00%	3 Missing :warning:
ibc-core/ics03-connection/types/src/error.rs	0.00%	3 Missing :warning:
ibc-derive/src/client_state.rs	70.00%	3 Missing :warning:
ibc-primitives/src/types/timestamp.rs	88.88%	3 Missing :warning:
...stkit/src/testapp/ibc/clients/mock/client_state.rs	0.00%	3 Missing :warning:
...ics07-tendermint/src/client_state/update_client.rs	88.88%	2 Missing :warning:
... and 11 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1119 +/- ## ========================================== + Coverage 66.51% 66.54% +0.02% ========================================== Files 209 209 Lines 20725 20617 -108 ========================================== - Hits 13785 13719 -66 + Misses 6940 6898 -42 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[rnbguy]

btw, I want to fix one more lint but the changes are too big. You can try it by running

cargo clippy --fix -- -W clippy::use_self