docs: Review and conform the Operations and Testing pages

[developerjamiu]

Phase 2 IA, PR 6 of 7 (tracked in #671): a review and conformance pass over the Operations pages (Caching, Logging, Security, Experimental) and the Testing pages, fixing several correctness bugs found during review.

What changed

• Caching: documented the localPrio and global cache accessors (only local was shown before); noun-first description.
• Logging: noun-first description; fixed a broken heading outline (H1 jumped to H3) and Title Case headings; removed em dashes.
• Security: renamed the page to "Security and TLS"; sentence-case headings; added an intro sentence to a bare-admonition open.
• Experimental: sentence-case shutdown-task headings; removed an em dash and a time-relative "new"; fixed a bare link and a sentence that opened with an inline code span.
• Testing: fixed the "Do" best-practices example to pass the sessionBuilder (not a built session) to endpoint calls; corrected an endpoint accessor (communicationExample), a containsAll matcher, code typos, the "practices" spelling, bare ./ links, trailing whitespace, and three weak page openings.

Verification

Checked against the current beta (Serverpod 4.0.0-beta.0): the cache accessors (caches.dart), logging config keys and defaults (config.dart), SecurityContextConfig params, the withServerpod config surface plus RollbackDatabase / AuthenticationOverride / flushEventQueue (serverpod_test), the experimental diagnostic-event and shutdown-task APIs, and that endpoint test calls take a TestSessionBuilder. Build passes locally.

Notes

• Move the Contribution Testing Guidelines to framework docs #629 is not included — it's a framework-repo move (contribution testing guidelines to the framework docs, plus closing PR feat: Add testing contribution guideline #229), not a serverpod_docs content change; handle separately.
• Left untouched pending framework confirmation (could not verify from source): the CLI --experimental-features options table and a couple of testing keys (server_test_tools_path, the log retention-count default).
• Structural deferrals stay for the final PR of this series: renaming the security-configuration.md and best-practises.md files, and the web-server numbering gap.

[Zfinix]

Approving pending comment resolution