Add cumulative resource score tracking across partial renders

[ianks]

Situation

Template#render unconditionally calls resource_limits.reset before rendering, which zeros render_score and assign_score. Since both {% render %} and {% include %} go through Template#render for each partial, the per-template scores reset on every partial invocation — making render_score_limit and assign_score_limit ineffective at bounding total work across partial renders. A template split across many small partials can execute unbounded cumulative work while each individual partial stays under the limit.

Execution

Added cumulative_render_score and cumulative_assign_score counters to ResourceLimits that piggyback on the existing increment_render_score/increment_assign_score methods but survive reset() calls. Two new optional limits (cumulative_render_score_limit, cumulative_assign_score_limit) are checked alongside the existing per-template limits. When unset (nil), the cumulative checks are skipped entirely — zero behavior change for existing users.

env = Liquid::Environment.build(
  default_resource_limits: {
    render_score_limit: 100_000,              # existing per-template limit (unchanged)
    cumulative_render_score_limit: 1_000_000, # new: caps total work across all partials
  },
)

Backwards compatibility

The existing render_score, assign_score, render_score_limit, assign_score_limit, and reset() behavior are completely unchanged — per-template scores still reset on every Template#render call exactly as before. The new cumulative fields default to nil (limits) and 0 (counters), so applications that never set cumulative_*_limit will never trigger the new code paths.

[Maaarcocr]

is this necessary? why?

[ianks]

makes it so we immediately stop rendering instead of letting each subsequent partial reset the flag and blow the limit again in a loop

[ianks]

might be better to address this in ResourceLimits#reset

[ianks]

done in a911767