Pin Rust version to 1.64.0

[alekece]

Description

This PR aims to pin the Rust version to 1.64.0 by using rust-toolchain file and unifying the Rust version in use both in the CI, dev machine and in docker container.

How was this PR tested?

1. Dev machine -> change the Rust version in rust-toolchain and run rustup show to check the version.
2. Dockerfile.rust -> run make build-nucliadb-rustbase_{arm,amd}64 and check the outputted value of RUST_VERSION.
3. CI -> just look the result of this PR

[codecov[bot]]

Codecov Report

Base: 67.26% // Head: 67.26% // No change to project coverage :thumbsup:

Coverage data is based on head (91660cf) compared to base (753464b). Patch has no changes to coverable lines.

:exclamation: Current head 91660cf differs from pull request most recent head 98b0932. Consider uploading reports for the commit 98b0932 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #323   +/-   ##
=======================================
  Coverage   67.26%   67.26%           
=======================================
  Files         209      209           
  Lines       14084    14084           
=======================================
  Hits         9474     9474           
  Misses       4610     4610           

Flag	Coverage Δ
node-sidecar	68.43% <ø> (ø)

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