feat(genetic): make the fitness cache size configurable (#1376)

The per-run fitness cache of the GENETIC optimizer is unbounded. It
grows with individuals x generations (~110k keys at 300 x 400, about
1.1 kB each, 1.6 kB with an EV) and adds 120-170 MB to the peak memory
of a run, while only 6-15 % of the lookups hit. On 512 MB boards this
is the largest part of the optimizer's memory.

Add optimization.genetic.fitness_cache_max_entries:

- None (default): unbounded, the previous behaviour.
- 0: no cache; every genome is evaluated.
- N > 0: at most N keys. The cache is then an OrderedDict and evicts
  the oldest key first (FIFO, O(1)); LRU would cost bookkeeping on
  every hit for a cache that rarely hits.

A cache hit returns exactly what the deterministic evaluation would
return, so the plan for a fixed seed is identical with any setting.

Co-authored-by: Christin <christin@BigBrother.bikini.bottom.zone>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Andreas <drbacke@gmx.de>

docs/_generated/configexample.md

@@ -258,6 +258,7 @@
                "individuals": 400,
                "generations": 400,
                "seed": null,
+               "fitness_cache_max_entries": null,
                "measurement_max_age_seconds": 300,
                "tail_horizon_hours": 48,
                "terminal_value_mode": "AUTO",

docs/_generated/configoptimization.md

@@ -30,6 +30,7 @@
                "individuals": 400,
                "generations": 400,
                "seed": null,
+               "fitness_cache_max_entries": null,
                "measurement_max_age_seconds": 300,
                "tail_horizon_hours": 48,
                "terminal_value_mode": "AUTO",
@@ -68,6 +69,7 @@
                "individuals": 400,
                "generations": 400,
                "seed": null,
+               "fitness_cache_max_entries": null,
                "measurement_max_age_seconds": 300,
                "tail_horizon_hours": 48,
                "terminal_value_mode": "AUTO",
@@ -173,6 +175,7 @@
 
 | Name | Type | Read-Only | Default | Description |
 | ---- | ---- | --------- | ------- | ----------- |
+| fitness_cache_max_entries | `Optional[int]` | `rw` | `None` | Maximum number of keys in the per-run fitness cache. None = unbounded (default), 0 = cache disabled, N > 0 = keep at most N keys and evict the oldest first. Every cached evaluation takes one or two keys. The cache only saves repeated evaluations; the result for a fixed seed is the same with any value. Limit it to cap memory on small devices. |
 | generations | `Optional[int]` | `rw` | `400` | Number of generations to evolve [>= 10]. Defaults to 400. |
 | horizon | `int` | `ro` | `N/A` | Number of optimization steps. |
 | horizon_hours | `int` | `rw` | `24` | The general time window within which the energy optimization goal shall be achieved [h]. Defaults to 24 hours. |
@@ -202,6 +205,7 @@
                "individuals": 300,
                "generations": 400,
                "seed": null,
+               "fitness_cache_max_entries": null,
                "measurement_max_age_seconds": 300,
                "tail_horizon_hours": 48,
                "terminal_value_mode": "AUTO",
@@ -230,6 +234,7 @@
                "individuals": 300,
                "generations": 400,
                "seed": null,
+               "fitness_cache_max_entries": null,
                "measurement_max_age_seconds": 300,
                "tail_horizon_hours": 48,
                "terminal_value_mode": "AUTO",