What does this PR do

Allow us to configure dynamic log levels via the environment variable COCO_LOG. (If it is not set, use the current default log level, INFO.)

Generally, it mirrors the behavior of env_logger. Syntax: COCO_LOG=<target>=<level>[,...], it is a log level triple sequence, separated by commas. Every log level triple consists of 3 parts:

1. target - which is the Rust crate or module name
2. = - an equal sign
3. level - the log level, which is case insensitive, "TRACE" is equivalent to "tRaCe"

target and level are optional:

• When the log level is omitted, e.g., COCO_LOG=coco_lib, the TRACE level will be used.
• When the target is omitted, the specified log level will apply to all the targets, i.e., all the Rust crates/modules

And the log level set for a specific target has higher priority than the log level set for all the targets.

Some examples

• I only want the logs that come from Coco-AI: COCO_LOG=coco_lib
• I only want the Coco-AI logs with log level higher than or equal to DEBUG: COCO_LOG=coco_lib=debug
• I want to disable Tauri's log; all the other logs should be accepted: COCO_LOG=trace,tauri=off
• I do not want logs: COCO_LOG=off or COCO_LOG=

Rationale for this change

Standards checklist

• The PR title is descriptive
• The commit messages are semantic
• Necessary tests are added
• Updated the release notes
• Necessary documents have been added if this is a new feature
• Performance tests checked, no obvious performance degradation