Timestamp, serialization, and deprecated cleanup

[Affie]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 59.09091% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.15%. Comparing base (4ce4d21) to head (d2667ce).

Files with missing lines	Patch %	Lines
src/Deprecated.jl	0.00%	6 Missing ⚠️
src/Common.jl	70.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1203      +/-   ##
===========================================
+ Coverage    68.34%   70.15%   +1.81%     
===========================================
  Files           36       36              
  Lines         2483     2416      -67     
===========================================
- Hits          1697     1695       -2     
+ Misses         786      721      -65     

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[dehann]

Suggested change

	**Temporal Uncertainty**: This single timestamp value is metadata and does not represent temporal uncertainty in non-parametric beliefs. For problems where time itself is a state variable requiring inference (e.g., using `SGal3` which includes temporal components), include time as part of your state type rather than relying on this metadata field.
	**Temporal Uncertainty**: This single timestamp value is metadata and does not represent temporal uncertainty. For problems where time itself is a state variable requiring inference (e.g., using `SGal3` which includes temporal components), include time as part of your state type rather than relying on this metadata field. Furthermore, the concept of "ClockPriors" is also at play for the API design changes relating to v2.
	**Future**: changing away from field name `timestamp` was deferred from v1.0 owing to resolution of older complexity of other fields being standardized; however, the desire for a better name exists and should be revisited in the v2 API. At time of writing, the best summary of the naming debate is captured here: https://github.com/JuliaRobotics/DistributedFactorGraphs.jl/issues/1087#issuecomment-3582252305. In the lead up to a new long term release (a.k.a semver major), a deprecation cycle will be used via semver minors to ensure users have an easy and macro-aided transition in the API.