Review Lodestar builder implementation plan

[krisoshea-eth]

Summary

• Adds the Lodestar EIP-7732 Builder implementation plan as raw Markdown for GitHub review.
• Mirrors the current live HackMD implementation plan from https://hackmd.io/j3T4poyWTFqcVAuaoWXiqA.

Review Scope

This PR is intended for review of docs/implementation-plan.md only.

The living technical note is intentionally not included yet. It will be opened separately after it is updated.

Validation

• Re-downloaded the live HackMD raw Markdown export before creating this branch.
• Confirmed the downloaded implementation plan matches the mirrored file byte-for-byte.
• Preserved HackMD hard-line-break trailing spaces so the GitHub file remains a raw Markdown mirror of the HackMD note.

[krisoshea-eth]

Added the follow-up Lodestar decisions and current implementation baseline in 17ee080:

• Keep the small waitForGenesis implementation duplicated in validator and Builder, with 404 treated as expected waiting and other errors logged as warnings.
• Do not add an unreachable Lodestar BN getGenesis 404 branch. Client handling remains useful for Teku and other BNs that expose the pre-genesis API.
• Reuse assertEqualParams from @lodestar/config now that refactor: move assertEqualParams from validator to config ChainSafe/lodestar#9725 is merged, and keep the Builder copy aligned with the validator behavior merged in fix: distinguish 404 from real errors when waiting for genesis ChainSafe/lodestar#9726.
• Keep request-auth constants and verification out of the core sidecar while feat: implement gloas builder api ChainSafe/lodestar#9594 and the staked Builder API path remain conditional.
• Record Marko’s draft package, CLI, keystore, signer, and genesis work as the starting point for CLI-01, SIGN-01, and API-01 without marking those issues Done before rebase, review, and current checks.

I also compared the amended plan with the original HackMD baseline. All original issue IDs, links, section coverage, and code-fence structure are retained; the substantive changes are limited to the accepted review feedback and the follow-up decisions above. b57d3e6 corrects the summary count to eight named conditional packages after adding the Grafana stretch package.

[linear-code]

LOD-23

LOD-37

LOD-24

LOD-25

LOD-26

LOD-11

LOD-27

LOD-28

LOD-29

LOD-30

LOD-31

LOD-32

LOD-33

LOD-1

LOD-34

LOD-35

LOD-21

LOD-36

LOD-38

LOD-39

LOD-13

LOD-40

LOD-41

LOD-42

LOD-43

LOD-7

LOD-44

LOD-8

LOD-2

LOD-9

LOD-4

LOD-6

LOD-10

LOD-15

LOD-14

LOD-17

LOD-3

LOD-5

LOD-19

LOD-22

LOD-12

LOD-16

LOD-18

LOD-20