Call Context Feature Flag

[Eathox]

• Move call context behind a feature flag which is enabled by default
• Move caller, source, mission and server getters to Context making ArmaCallContext an implementation detail
• Implement Default for when call is used in testing removing the need for unwrap on context fields. Only relevant to testing as Arma should always pass values.

[codecov[bot]]

Codecov Report

Merging #41 (78d6fe4) into main (40cd678) will increase coverage by 0.08%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   89.72%   89.81%   +0.08%     
==========================================
  Files          28       28              
  Lines        2929     2935       +6     
==========================================
+ Hits         2628     2636       +8     
+ Misses        301      299       -2     

Impacted Files	Coverage Δ
arma-rs-example/src/call_context.rs	100.00% <100.00%> (ø)
arma-rs-example/src/lib.rs	98.52% <100.00%> (ø)
arma-rs-proc/src/lib.rs	100.00% <100.00%> (ø)
arma-rs/src/context/call.rs	100.00% <100.00%> (ø)
arma-rs/src/context/mod.rs	92.17% <100.00%> (+0.82%)	:arrow_up:
arma-rs/src/lib.rs	98.04% <100.00%> (+0.01%)	:arrow_up:
arma-rs/src/testing.rs	83.14% <100.00%> (+0.79%)	:arrow_up:

... and 1 file with indirect coverage changes