Fix tail log methods returning untyped array responses

[guillaumedelre]

Closes #1, closes #34.

## Core fix: tail log methods

tailProcessStdoutLog() and tailProcessStderrLog() were routed through
__call() and returned a raw array [bytes, offset, overflow] with no
indication of what each index contained. This made the methods unusable
without reading the Supervisor API documentation directly.

- Introduce TailLogInterface and TailLog value object following the
  existing ReloadResult pattern
- Add explicit tailProcessStdoutLog() / tailProcessStderrLog() methods
  on Supervisor and SupervisorInterface, returning TailLogInterface
- Add TailLogSpec (5 examples) and SupervisorSpec coverage for both methods
- Document the offset-based iteration pattern in README and clarify that
  FailedException (fault 30) is thrown when the process log file does
  not exist yet
- Remove outdated notice about the PHP XML-RPC extension

## Typed DTO for getState()

getState() previously returned a raw array via __call(). Introduce
StateInfo and StateInfoInterface (statecode + statename), following the
same pattern as TailLog. Update getServiceState() to delegate to
getState()->getStateCode().

## Bug fixes

- Process::checkState() and Supervisor::checkState(): return false
  explicitly when ServiceStates/ProcessStates::tryFrom() yields null for
  an unknown int, instead of comparing an enum to null silently
- Remove unused ReloadExceptions import from Supervisor and
  SupervisorInterface (class does not exist)
- isConnected(): log the exception message at debug level instead of
  discarding it silently
- Process::offsetGet(): throw OutOfBoundsException on unknown key
  instead of returning null silently

## Code quality

- Normalise @method docblocks: integer/boolean -> int/bool
- Fix duplicate docblock on ProcessInterface::getState()
- Remove unused ReturnTypeWillChange import from Process
- Set minimum-stability to stable in composer.json
- Annotate array parameters with generic types for PHPStan level 8
  compatibility (array<int, mixed>, array<string, mixed>, list<string>,
  array shapes, class-string<SupervisorException>)
- Extend CI matrix to PHP 8.1, 8.2, 8.3 and 8.4

## Tests

- Add ReloadResultSpec: fromReloadConfig() parsing, null-safe fallback,
  getAffected() merge (7 examples)
- Add 5 specs for reloadAndApplyConfig(): removed groups, modified
  groups with and without stopModifiedGroups flag, added groups with and
  without startNewProcesses flag
- Add StateInfoSpec (5 examples)