#293 Retry gist updates and make history merges idempotent

[sanelli]

Summary

• Retry gh gist edit up to 5 times with a random 2–10s delay to handle intermittent HTTP 409 failures on main-merge.
• Make coverage and benchmark history merges idempotent by replacing rows for the same Mappa version before republishing.
• Allow omitting coverage baseline/final steps for Scripts/Documentation/cursor-rule-only work; bump to 10.2.0-alpha.30.

Test plan

• Review Scripts/GistHelpers.ps1 retry and version-merge helpers
• Dry-run UpdateCodeCoverageGists.ps1 -DryRun / UpdateBenchmarkGists.ps1 -DryRun with local history tables if available
• Confirm CI version check passes (CheckVersionIncrease.ps1)
• After merge, re-run main-merge (or simulate) and confirm gist history does not duplicate the same version

Closes #293

[github-actions]

Code coverage

Compared against the latest published coverage history from the code coverage gist.

Metric	Baseline	PR	Δ	Trend
Line	98.4%	98.4%	0	=
Branch	90.6%	90.6%	0	=
Method	100%	100%	0	=

No coverage metric dropped by more than 1 percentage point(s) versus baseline.

Benchmarks

AutoMapper is the BenchmarkDotNet ratio baseline. Absolute values are mean time in nanoseconds and allocated bytes. Ratio columns are competitor / Mappa as a percentage (n/a when either side is missing or Mappa is zero).

Benchmark	Automapper Mean (ns)	Automapper Allocated (B)	Mapster Mean (ns)	Mapster Allocated (B)	Mapperly Mean (ns)	Mapperly Allocated (B)	Mappa Mean (ns)	Mappa Allocated (B)	Automapper/Mappa Time	Automapper/Mappa Alloc	Mapperly/Mappa Time	Mapperly/Mappa Alloc	Mapster/Mappa Time	Mapster/Mappa Alloc
ArrayToListBenchmark	68.09	32	76596.32	194456	7742.17	38456	7573.84	38456	0.9%	0.1%	102.2%	100%	1011.3%	505.7%
DictionaryBenchmark	101920	185221.12	89470	214364.16	11050	46018.56	13000	58316.8	784%	317.6%	85%	78.9%	688.2%	367.6%
FastListToArrayBenchmark	n/a	n/a	79551	194426.88	8141	38420.48	8320	38420.48	n/a	n/a	97.8%	100%	956.1%	506.1%
IQueryableProjectionBenchmark	635600	31784.96	606500	31016.96	621300	33187.84	614100	32983.04	103.5%	96.4%	101.2%	100.6%	98.8%	94%
ListToArrayBenchmark	n/a	n/a	79089	194426.88	7725	38420.48	8537	38420.48	n/a	n/a	90.5%	100%	926.4%	506.1%
ListToHashSetBenchmark	269	5765.12	2258.3	5765.12	2071.2	5806.08	1536.6	5765.12	17.5%	100%	134.8%	100.7%	147%	100%
NestedDtoBenchmark	92335	225320.96	95026	227471.36	7979	38942.72	7497	38942.72	1231.6%	578.6%	106.4%	100%	1267.5%	584.1%

Benchmark trends (Mappa)

Lower is better. Compared against the latest published Mappa-only rows from MAPPA-BENCHMARK-HISTORY.md.

Benchmark	Measure	Baseline	PR	Δ	Trend
ArrayToListBenchmark	TIME_NS	6927.86	7573.84	+645.98	▼
ArrayToListBenchmark	ALLOC_B	38456	38456	0	=
DictionaryBenchmark	TIME_NS	13130	13000	-130	▲
DictionaryBenchmark	ALLOC_B	58316.8	58316.8	0	=
ListToArrayBenchmark	TIME_NS	6630	8537	+1907	▼
ListToArrayBenchmark	ALLOC_B	38420.48	38420.48	0	=
FastListToArrayBenchmark	TIME_NS	6717	8320	+1603	▼
FastListToArrayBenchmark	ALLOC_B	38420.48	38420.48	0	=
IQueryableProjectionBenchmark	TIME_NS	593000	614100	+21100	▼
IQueryableProjectionBenchmark	ALLOC_B	32983.04	32983.04	0	=
NestedDtoBenchmark	TIME_NS	6773	7497	+724	▼
NestedDtoBenchmark	ALLOC_B	38942.72	38942.72	0	=
ListToHashSetBenchmark	TIME_NS	2418	1536.6	-881.4	▲
ListToHashSetBenchmark	ALLOC_B	5765.12	5765.12	0	=