chore(docs): trim moduledocs — drop EVM Concepts and Elixir Learning Notes

[mw2000]

Summary

• Removes the `## EVM Concepts` (yellow-paper / EIP recaps duplicating public references) and `## Elixir Learning Notes` (Elixir tutorial content) sections from every `@moduledoc` in `lib/`. Neither belongs in API documentation.
• 43 files touched, -780 LOC net (947 deletions, 167 insertions).
• Lead-in descriptions and API-relevant content (field tables, wire-encoding notes, examples, doctests) are preserved. Function-level `@doc`s untouched.
• Where deletions left the lead-in too thin, a tight 1–3 sentence factual replacement was written grounded in the code (e.g. `block/withdrawal.ex`, `system_contracts/block_hashes.ex`, `world_state.ex`).

Test plan

• `mix compile` clean
• `mix format --check-formatted` clean
• `mix credo --strict` — 1175 mods/funs, found no issues
• `mix test` — 4 doctests, 617 tests, 0 failures
• `grep -r "## EVM Concepts\|## Elixir Learning Notes" lib/` returns nothing

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