Fix and clean up constant comparisons flagged by CodeQL java/constant-comparison

[vharseko]

Summary

Resolves the 19 open java/constant-comparison CodeQL alerts: 2 real defects
fixed, 12 provably-constant (dead) comparisons removed in code
(behaviour-identical, so the alerts are cleared at the source), and 5 dismissed
as won't fix (intentional defensive/readable code).

Real bugs (2)

Module	File	Defect
persistit/ui	ManagementTableModel	Column-removal loop for (i = _displayedColumnCount; --i >= count;) inside if (count > _displayedColumnCount) — body never executed, so surplus table columns were never removed. Bounds were swapped.
json-schema/cli	Main	Verbose validation tested valid.length == 0 (a boolean[1], always false) and never set the flag true → "OK - Object is valid!" never printed. Init flag to true, test valid[0].

Dead / redundant comparisons removed (12, behaviour-identical)

Module	File	Dead comparison
persistit/core	TransactionPlayer	Replay loop re-checked type != TX.TYPE without re-reading type. Now re-reads type per continuation record so the check is live and consistent with the recordSize check.
persistit/core	LongRecordHelper	if (count > MAX_LONG_RECORD_CHAIN) nested inside an identical one — flattened.
persistit/core	KeyParser	else-branch re-tested if (c == '\\'), unreachable there (backslash handled above).
persistit/core	Key	return i < _size ? i + 1 : -1 → i < _size always true → return i + 1.
persistit/core	Key	Removed if (index < 0) break; inside a for (…; index >= 0; …) loop.
commons/util	JsonValue	Dropped && index >= 0 after the preceding if (index < 0) throw.
commons/json-fluent	JsonValue	Same && index >= 0 (legacy copy).
persistit/ui	AdminUIBufferPanel	Dropped _bufferPoolIndex >= 0 && after the index is normalised to 0 two lines above.
persistit/core	IOMeter	Dropped op >= 0 && after if (op == -1) break.
persistit/core	FastIndex	Removed vestigial faultAt var and its if (faultAt < 0) guards (assigned then immediately returned, never read).
persistit/core	Buffer	Removed a dead diagnostic-dump clamp if (keep < TAILBLOCK_HDR_SIZE_DATA && keep > tbSize) (never holds; fill loop already handles keep > tbSize).

Behaviour

Only two behaviours change, both to fix the bugs above (columns now removed; verbose
success now printed). Everything else is behaviour-identical removal of
provably-constant sub-expressions. TransactionPlayer now re-reads type on each
continuation record — a live re-validation that was previously dead; every record is
already type-validated in the first pass, so this only tightens defence-in-depth.

Not in this PR (dismissed as won't fix, 5)

Intentional code where the constant sub-expression is deliberate:
LongRecordHelper and Key.maxStorableKeySize defensive assertions/clamps,
Buffer page-integrity bounds and a provable invariant on the hot key-search path,
and the explicit HTTP status-family range ladder in Status.

Testing

mvn -o -pl persistit/core,persistit/ui,commons/json-schema/cli,commons/util/util,commons/json-fluent compile — all modules compile.
commons/util JsonValueTest + JsonValueFunctionsTest (96) and json-fluent JsonValueTest (5) pass, covering the get(int) change. (persistit unit tests are skipped in the offline build environment.)