Modernize the lint and format toolchain (eslint, prettier, solhint)

[mswilkison]

Both packages are several majors behind on everything that lints or formats:

Package	random-beacon	ecdsa	Current
eslint	^7.32.0	^7.32.0	10.8.0 — long past EOL
prettier	^2.4.1	^2.5.1	3.9.6
solhint	^3.3.6	^3.3.6	6.2.3
prettier-plugin-solidity	^1.0.0-beta.18	^1.0.0-beta.19	2.3.1 — four-year-old beta

Probably three PRs rather than one, since the costs differ:

• eslint 7 → 10 crosses the flat-config break at 9, and @thesis-co/eslint-config (a git tarball) has to come along. This is the real work.
• prettier 2 → 3 reformats both trees. Best as its own commit containing nothing else, so review is git diff --stat. Note prettier 3 changed the default trailingComma to "all".
• solhint 3 → 6 plus solhint-config-keep, also a git tarball.

Both packages currently pass lint with 0 errors and a pile of warnings (18 + 13 in random-beacon, 103 + 9 in ecdsa). Worth deciding whether to fix or formally accept those while in here.

Same work in tbtc-v2: threshold-network/tbtc-v2#1077.

[linear]

ENG-699

[mswilkison]

Closing PR: #4304, with prerequisite PRs #4302 (ESLint 10 flat configs) and #4303 (Prettier 3 plus a separate formatting-only commit). The Git-pinned shared lint configs are replaced with explicit local policy. All lint/format checks pass; existing warnings remain deliberately non-blocking, with the error rules preserved. Fresh TypeChain generation succeeds, all 159 compiled contract ABIs/runtimes match after stripping compiler metadata, and all 108 reformatted TypeScript files preserve emitted JavaScript behavior. Coordinate #4205 and #4217 with this stack.

The issue is left open until the closing PR and its prerequisites land.

Follow-up #4306 preserves generated TypeChain overloads in the lint TypeScript programs while generated output remains excluded from lint targets.