Feature: Support Named Credentials for REST log saves

[jcd1991]

PR description

Closes #996.

Related to #761 and builds on the upstream fix in #995. This change keeps the #995 behavior as the source of truth: non-REST logging no longer resolves a session ID, while REST retains the synchronous session-ID fallback for backwards compatibility. Machine-to-machine contexts can require a Named Credential explicitly.

Summary

• Added LoggerParameter.RestApiNamedCredential and LoggerParameter.RestApiRequireNamedCredential Custom Metadata records.
• Added Named Credential endpoint construction with optional callout: prefix normalization and no manually supplied Authorization header.
• Added a catchable configuration error when a Named Credential is required but missing.
• Chunked REST sObject Collections requests by Salesforce's 200-record limit, serialized request size, and remaining callout budget.
• Removed quadratic serialization and buffer-removal behavior.
• Validated HTTP status, JSON shape, result count, item-level success, errors, and returned IDs.
• Defined at-least-once retry semantics for failed or ambiguous chunks.
• Added positive, negative, malformed-response, mixed-result, retry, payload-size, callout-budget, handler-reordering, fallback, and System.UserInfo.getSessionId() throws System.UnexpectedException #761 regression tests.
• Updated README and Apex configuration documentation.

Package and security notes

• Named Credential, External Credential, endpoint secrets, and org-specific authentication metadata are intentionally not included in package source.
• Subscribers must create and authorize the Named Credential in their own org.
• The existing managed-package release pipeline should generate the managed-package source and package version after review; no package version is created by this local draft.

Test plan

• Focused Salesforce suite: 562/562 passed.
• Full Salesforce suite: 1,304/1,304 passed.
• Repository-wide LWC suite: 19 suites, 336/336 passed.
• Apex PMD scan: 0 violations.
• Prettier verification and git diff --check: passed.
• The local Developer Edition verified Named Credential routing with an org-only no-auth Named Credential; authenticated External Credential exchange remains a sandbox/scratch-org release verification step.

Release checklist

• Run the repository CI scratch-org matrix and Codecov workflow.
• Run the managed/unlocked package-version automation required by the release pipeline; no package version is created by this local draft.
• Validate a real authenticated Named Credential/External Credential exchange in a sandbox or scratch org. The local Developer Edition test intentionally used an org-only no-auth Named Credential and verified routing, not subscriber authentication.
• Re-run the Apex documentation generator in the CI/build environment. The local docs verifier reported the repository's known PowerShell/apexdocs symlink warning, so generated-doc freshness is not claimed as fully verified locally.

Branch

• Base: main
• Head: feature/996-rest-named-credential
• Local commit: 7bdae54