Add parser for i64

[koalo]

Signed 64 is for example used for TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME.

[koalo]

I have a few patches in the pipeline to add support for the TAPRIO Qdisc ( https://man7.org/linux/man-pages/man8/tc-taprio.8.html ) required in the context of time-sensitive networking to rust-netlink. This is the first and most trivial one.

[koalo]

Just as rust-netlink/netlink-packet-core#22 this currently blocks me from providing further contributions to rust-netlink that I already have in my pipeline.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 34.60%. Comparing base (5e39d65) to head (c01aa44).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/parsers.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
- Coverage   35.18%   34.60%   -0.58%     
==========================================
  Files           3        3              
  Lines         361      367       +6     
==========================================
  Hits          127      127              
- Misses        234      240       +6     

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