chore: move some trace utilities to isomorphic

[dgozman]

This way, we can reuse them in Node.js environment.

Drive-by: to avoid confusion, rename TraceModel -> TraceLoader and MultiTraceModel -> TraceModel.

[github-actions]

Test results for "MCP"

2 failed
❌ [webkit] › mcp/generator.spec.ts:282 › should respect custom test id @mcp-ubuntu-latest
❌ [webkit] › mcp/http.spec.ts:73 › http transport (config) @mcp-ubuntu-latest

2608 passed, 116 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

1 fatal errors, not part of any test

10 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1079 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node18`
⚠️ [firefox-page] › page/page-wait-for-function.spec.ts:104 › should work with strict CSP policy `@firefox-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/browsercontext-cookies-third-party.spec.ts:319 › add 'Partitioned;' cookie via API `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/browsercontext-reuse.spec.ts:94 › reuse launch › should re-add binding after reset `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/proxy.spec.ts:93 › should proxy local network requests › with other bypasses › localhost `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/selector-generator.spec.ts:80 › selector generator › should trim text `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/trace-viewer.spec.ts:99 › should open two trace viewers `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-library] › library/tracing.spec.ts:68 › should use the correct title for event driven callbacks `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-page] › page/page-filechooser.spec.ts:24 › should upload multiple large files `@webkit-ubuntu-22.04-node18`
⚠️ [webkit-page] › page/page-set-input-files.spec.ts:146 › should upload large file `@webkit-ubuntu-22.04-node18`

40331 passed, 787 skipped

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Merge workflow run.